200 results on '"Enrique R. Batista"'
Search Results
102. Origins of the Regioselectivity in the Lutetium Triflate Catalyzed Ketalization of Acetone with Glycerol: A DFT Study
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Weizhong Chen, Jin Kyung Kim, Caroline B. Hoyt, Louis A. Silks, Ryszard Michalczyk, Aaron W. Pierpont, Richard L. Martin, John C. Gordon, Ruilian Wu, and Enrique R. Batista
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chemistry.chemical_compound ,chemistry ,Solketal ,Acetone ,Glycerol ,Regioselectivity ,Organic chemistry ,General Chemistry ,Lewis acids and bases ,Selectivity ,Trifluoromethanesulfonate ,Catalysis - Abstract
We describe DFT computations that address the regioselective preference toward the five-membered ring product 1,3-dioxolane (solketal) over the six-membered-ring product (1,3-dioxane) during Lu(OTf)3-catalyzed ketalization of acetone with glycerol. When ketalization occurs via the internal (secondary) −OH group of glycerol, only solketal production should be possible due to the symmetry of the intermediates. Ketalization via the terminal −OH group of glycerol is predicted to occur in a different manner than the conventionally proposed ketalization mechanism. A constrained hemiketal intermediate is invoked to explain the selectivity for solketal formation.
- Published
- 2015
103. Reactions of Deuterated Methanol (CD3OD) on Fe3O4(111)
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George W. Flynn, Kwang Taeg Rim, Denis V. Potapenko, Zhisheng Li, Maria Flytzani-Stephanopoulos, Xiaodong Wen, Enrique R. Batista, and Richard M. Osgood
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Crystal ,chemistry.chemical_compound ,General Energy ,chemistry ,Analytical chemistry ,Physical chemistry ,Deuterated methanol ,Partial oxidation ,Physical and Theoretical Chemistry ,Decomposition ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
We report an experimental and theoretical investigation of the decomposition (partial oxidation) of deuterated methanol (CD3OD) on a single-crystal Fe3O4(111) surface. The crystal surface contains ...
- Published
- 2015
104. On the Origin of Covalent Bonding in Heavy Actinides
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Matthew Urban, Enrique R. Batista, Jing Su, Ping Yang, Morgan Luckey, Morgan P. Kelley, and Jenifer C. Shafer
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010405 organic chemistry ,Chemistry ,Ligand ,Nuclear Theory ,Ionic bonding ,General Chemistry ,Orbital overlap ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Specific orbital energy ,Colloid and Surface Chemistry ,Atomic orbital ,Chemical physics ,Covalent bond ,Condensed Matter::Strongly Correlated Electrons ,Molecular orbital ,Degeneracy (biology) ,Atomic physics ,Nuclear Experiment - Abstract
Recent reports have suggested the late actinides participate in more covalent interactions than the earlier actinides, yet the origin of this shift in chemistry is not understood. This report considers the chemistry of actinide dipicolinate complexes to identify why covalent interactions become more prominent for heavy actinides. A modest increase in measured actinide:dipicolinate stability constants is coincident with a significant increase in An 5f energy degeneracy with the dipicolinate molecular orbitals for Bk and Cf relative to Am and Cm. While the interactions in the actinide-dipicolinate complex are largely ionic, the decrease in 5f orbital energy across the series manifests in orbital-mixing and, hence, covalency driven by energy degeneracy. This observation suggests the origin of covalency in heavy actinide interactions stems from the degeneracy of 5f orbitals with ligand molecular orbitals rather than spatial orbital overlap. These findings suggest that the limiting radial extension of the 5f orbitals later in the actinide series could make the heavy actinides ideal elements to probe and tune effects of energy degeneracy driven covalency.
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- 2017
105. Bonding in Uranium(V) Hexafluoride Based on the Experimental Electron Density Distribution Measured at 20 K
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Stefan G. Minasian, Christopher G. Gianopoulos, Vladimir V. Zhurov, Enrique R. Batista, Christian Jelsch, A. Alan Pinkerton, University of Toledo, Lawrence Berkeley National Laboratory [Berkeley] (LBNL), Los Alamos National Laboratory (LANL), Cristallographie, Résonance Magnétique et Modélisations (CRM2), and Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS)
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Diffraction ,Electron density ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Inorganic Chemistry ,Electron density distribution ,chemistry.chemical_compound ,Hexafluoride ,[CHIM.CRIS]Chemical Sciences/Cristallography ,[CHIM.COOR]Chemical Sciences/Coordination chemistry ,Physical and Theoretical Chemistry ,010405 organic chemistry ,Experimental model ,structure of UF6 ,Bonding in actinides ,Uranium ,Chemical Engineering ,0104 chemical sciences ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Formalism (philosophy of mathematics) ,charge density ,chemistry ,Covalent bond ,Inorganic & Nuclear Chemistry ,Atomic physics ,Other Chemical Sciences ,Physical Chemistry (incl. Structural) - Abstract
© 2017 American Chemical Society. The electron density distribution of [PPh4][UF6] was obtained from high-resolution X-ray diffraction data measured at 20 K. The electron density was modeled with an augmented Hansen-Coppens multipolar formalism. Topological analysis reveals that the U-F bond is of incipient covalent nature. Theoretical calculations add further support to the bonding description gleaned from the experimental model. The impact of the uranium anomalous dispersion terms on the refinement is also discussed.
- Published
- 2017
106. MoD-QM/MM Structural Refinement Method: Characterization of Hydrogen Bonding in the Oxytricha nova G-Quadruplex
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J. Patrick Loria, Junming Ho, Enrique R. Batista, José A. Gascón, Christina Ragain, Victor S. Batista, and Michael B. Newcomer
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biology ,Chemistry ,Hydrogen bond ,Chemical shift ,Ab initio ,Thermodynamics ,Oxytricha ,G-quadruplex ,biology.organism_classification ,Article ,Computer Science Applications ,QM/MM ,Crystallography ,Proton NMR ,Physical and Theoretical Chemistry ,Quantum - Abstract
A generalization of the Moving-Domain Quantum Mechanics/Molecular Mechanics (MoD-QM/MM) hybrid method [Gascon, J. A.; Leung, S. S. F.; Batista, E. R.; Batista, V. S. J. Chem. Theory Comput. 2006, 2, 175-186] is introduced to provide a self-consistent computational protocol for structural refinement of extended systems. The method partitions the system into molecular domains that are iteratively optimized as quantum mechanical (QM) layers embedded in their surrounding molecular environment to obtain an ab initio quality description of the geometry and the molecular electrostatic potential of the extended system composed of those constituent fragments. The resulting methodology is benchmarked as applied to model systems that allow for full QM optimization as well as through refinement of the hydrogen bonding geometry in Oxytricha nova guanine quadruplex for which several studies have been reported, including the X-ray structure and NMR data. Calculations of (1)H NMR chemical shifts based on the gauge independent atomic orbital (GIAO) method and direct comparisons with experiments show that solvated MoD-QM/MM structures, sampled from explicit solvent molecular dynamics simulations, allow for NMR simulations in much improved agreement with experimental data than models based on the X-ray structure or those optimized using classical molecular mechanics force fields.
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- 2014
107. Electronic structure and O K-edge XAS spectroscopy of U3O8
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Stosh A. Kozimor, Brian L. Scott, Scott R. Daly, Anthony K. Burrell, Xiaodong Wen, Tolek Tyliszczak, David K. Shuh, Richard L. Martin, Stefan G. Minasian, Kevin S. Boland, Thomas M. McCleskey, Steven D. Conradson, Matthias W. Löble, Enrique R. Batista, and Eve Bauer
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X-ray absorption spectroscopy ,Radiation ,Valence (chemistry) ,Absorption spectroscopy ,Chemistry ,Analytical chemistry ,Electronic structure ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Hybrid functional ,K-edge ,Density functional theory ,Physical and Theoretical Chemistry ,Spectroscopy - Abstract
Understanding the uranium 5f/6d orbital mixing with oxygen 2p valence orbitals in uranium oxides is important for advancing nuclear technology. Unfortunately, U–O orbital mixing is difficult to probe experimentally. In this manuscript, U–O bonding is evaluated in U 3 O 8 using O K-edge X-ray absorption spectroscopy (XAS). To confirm that the O K-edge XAS spectra were correct and did not contain contributions from surface contamination, three different sample types were investigated using three unique detection methods. Specifically an epitaxial film of U 3 O 8 deposited on Al 2 O 3 (PAD-U 3 O 8 ) was probed using grazing-incidence fluorescence yield (GIFY) detection, a bulk powder of α-phase U 3 O 8 was analyzed with fluorescence yield (FY) detection at normal incidence, and particles of α-phase U 3 O 8 were studied in transmission mode using a scanning transmission X-ray microscope (STXM). Experimental spectra have been presented in the context of previously published computational results from DFT using the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid functional. Overall, the comparative analyses of PAD-U 3 O 8 and α-phase U 3 O 8 samples enabled identification of unique signatures associated with oxygen 2p orbital mixing with both U V and U VI 5f and 6d valence orbitals.
- Published
- 2014
108. How Does Nishibayashi’s Molybdenum Complex Catalyze Dinitrogen Reduction to Ammonia?
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Yong-Hui Tian, Enrique R. Batista, and Aaron W. Pierpont
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Chemistry ,Ligand ,chemistry.chemical_element ,Photochemistry ,Combinatorial chemistry ,Catalysis ,Inorganic Chemistry ,Metal ,Ammonia ,chemistry.chemical_compound ,Delocalized electron ,Oxidation state ,Molybdenum ,visual_art ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Bimetallic strip - Abstract
Recently, Nishibayashi et al. reported a dimolybdenum-dinitrogen complex that is catalytic for complete reduction of dinitrogen to ammonia. This catalyst is different from the Schrock molybdenum catalyst in two fundamental aspects: it contains two metal centers, and the oxidation state is Mo(0) instead of Mo(III). We show that a remarkable feature of the bimetallic complex is the bond-mediated delocalized electronic states, resulting from the two metal centers bridged by a dinitrogen ligand. Using first-principles calculations, we found that this property makes the bimetallic complex the effective catalyst, as opposed to the originally postulated monometallic fragment. A favorable reaction pathway is identified, and the nature of the intermediates is examined. Furthermore, studies of the intermediate states led us to propose possible deactivation processes of the catalyst. The finding that the central bimetallic unit (Mo-N2-Mo) is relevant for catalytic activity may provide a guideline for the development of more efficient dinitrogen-reducing catalysts.
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- 2014
109. New evidence for 5f covalency in actinocenes determined from carbon K-edge XAS and electronic structure theory
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Enrique R. Batista, David Clark, David K. Shuh, Tolek Tyliszczak, Kevin S. Boland, Richard L. Martin, Stefan G. Minasian, Stosh A. Kozimor, and Jason M. Keith
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chemistry.chemical_compound ,X-ray absorption spectroscopy ,Uranocene ,K-edge ,chemistry ,Atomic orbital ,Absorption spectroscopy ,Molecule ,Molecular orbital ,General Chemistry ,Electronic structure ,Atomic physics ,Molecular physics - Abstract
Evidence for metal–carbon orbital mixing in thorocene and uranocene was determined from DFT calculations and carbon K-edge X-ray absorption spectra (XAS) collected with a scanning transmission X-ray microscope (STXM). Both the experimental and computational results showed that the 5f orbitals engaged in significant δ-type mixing with the C8H82− ligands, which increased as the 5f orbitals dropped in energy on moving from Th4+ to U4+. The first experimental evidence for extensive ϕ-orbital interactions has been provided by the C K-edge XAS analysis of thorocene; however, ϕ-type covalency in uranocene was negligible. The results highlighted two contrasting trends in orbital mixing from one pair of highly symmetric molecules, and showed that covalency does not increase uniformly for different molecular orbital interactions with later actinides.
- Published
- 2014
110. Rücktitelbild: [Am(C 5 Me 4 H) 3 ]: An Organometallic Americium Complex (Angew. Chem. 34/2019)
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Jing Su, Stefanie Dehnen, Scott R. Daly, Stosh A. Kozimor, Brian L. Scott, Enrique R. Batista, Andrew J. Gaunt, William J. Evans, Anastasia V. Blake, Thomas E. Albrecht-Schmitt, Niels Lichtenberger, Ping Yang, and Conrad A. P. Goodwin
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chemistry ,Polymer chemistry ,chemistry.chemical_element ,Americium ,General Medicine - Published
- 2019
111. Back Cover: [Am(C 5 Me 4 H) 3 ]: An Organometallic Americium Complex (Angew. Chem. Int. Ed. 34/2019)
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Andrew J. Gaunt, Stefanie Dehnen, Niels Lichtenberger, Ping Yang, Scott R. Daly, Brian L. Scott, Conrad A. P. Goodwin, Stosh A. Kozimor, William J. Evans, Anastasia V. Blake, Enrique R. Batista, Thomas E. Albrecht-Schmitt, and Jing Su
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Chemistry ,INT ,Physical chemistry ,chemistry.chemical_element ,Cover (algebra) ,Americium ,General Chemistry ,Catalysis - Published
- 2019
112. Cover Feature: Linked Picolinamide Nickel Complexes as Redox Carriers for Nonaqueous Flow Batteries (ChemSusChem 7/2019)
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Brian L. Scott, Ivan A. Popov, Gabriel A. Andrade, Sandip Maurya, Ping Yang, Benjamin L. Davis, Rangachary Mukundan, Terry Chu, and Enrique R. Batista
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Nickel ,General Energy ,Materials science ,Chemical engineering ,chemistry ,Flow (mathematics) ,Feature (computer vision) ,General Chemical Engineering ,Environmental Chemistry ,chemistry.chemical_element ,General Materials Science ,Cover (algebra) ,Redox - Published
- 2019
113. Coordination Chemistry of +3 Actinium
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Kevin D. John, Benjamin W. Stein, Amanda Morgenstern, Laura M. Lilley, Veronika Mocko, Enrique R. Batista, Stosh A. Kozimor, and Eva R. Birnbaum
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chemistry.chemical_classification ,Actinium ,Radiological and Ultrasound Technology ,chemistry ,Computational chemistry ,chemistry.chemical_element ,Radiology, Nuclear Medicine and imaging ,Coordination complex - Published
- 2019
114. Effect of trans - and cis -isomeric defects on the localization of the charged excitations in π-conjugated organic polymers
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Iffat Nayyar, Darryl L. Smith, Sergei Tretiak, Enrique R. Batista, Avadh Saxena, and Richard L. Martin
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chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Solvation ,Electron ,Polymer ,Conjugated system ,Condensed Matter Physics ,Polaron ,chemistry ,Computational chemistry ,Chemical physics ,Lattice (order) ,Materials Chemistry ,Spatial localization ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
We use the long-range-corrected hybrid density functional theory models to study the effect of various conformational distortions of weak-trans and strong-cis nature on the spatial localization of charged states in poly(p-phenylene vinylene) (PPV) and its derivative poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV). The extent of self-trapping of positive (P+) and negative (P−) polarons is observed to be highly sensitive to molecular conformation that, in turn, controls the distribution of atomic charges within the polymers. It is shown that, to reach good agreement with recent experimental data on lattice distortion for P+ and P− excitations, the polarization of the medium plays a critical role. The introduction of weak-trans defects along the MEH-PPV chain breaks the observed symmetry for P+ and P− excitations. The P− states exhibit more spatial localization owing to lattice relaxation than their vacuum counterparts in contrast to P+. These observations suggest higher mobilities of holes than that of electrons in MEH-PPV, in agreement with the experimental observations. The predicted binding, reorganization, and solvation energies for PPV and MEH-PPV are analyzed for this difference in the response behavior of holes and electrons for trans and cis distortions. This study allows for a better understanding of charge-transport and photophysical properties in π-conjugated organic materials by analyzing their underlying structure–property correlations. © 2013 Wiley Periodicals, Inc.1 J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 935–942
- Published
- 2013
115. Tetrahalide Complexes of the [U(NR)2]2+ Ion: Synthesis, Theory, and Chlorine K-Edge X-ray Absorption Spectroscopy
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Trevor W. Hayton, Marianne P. Wilkerson, Kevin S. Boland, Brian L. Scott, Richard L. Martin, Stefan G. Minasian, Ping Yang, David K. Shuh, Robert E. Jilek, Steven D. Conradson, James M. Boncella, Molly M. MacInnes, David Clark, Enrique R. Batista, Stosh A. Kozimor, Angela C. Olson, and Liam P. Spencer
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Models, Molecular ,X-ray absorption spectroscopy ,Absorption spectroscopy ,Chemistry ,Inorganic chemistry ,Halide ,General Chemistry ,Electronic structure ,Time-dependent density functional theory ,Imides ,Biochemistry ,Catalysis ,Ion ,Crystallography ,X-Ray Absorption Spectroscopy ,Colloid and Surface Chemistry ,K-edge ,Organometallic Compounds ,Quantum Theory ,Uranium ,Density functional theory ,Chlorine - Abstract
Synthetic routes to salts containing uranium bis-imido tetrahalide anions [U(NR)(2)X(4)](2-) (X = Cl(-), Br(-)) and non-coordinating NEt(4)(+) and PPh(4)(+) countercations are reported. In general, these compounds can be prepared from U(NR)(2)I(2)(THF)(x) (x = 2 and R = (t)Bu, Ph; x = 3 and R = Me) upon addition of excess halide. In addition to providing stable coordination complexes with Cl(-), the [U(NMe)(2)](2+) cation also reacts with Br(-) to form stable [NEt(4)](2)[U(NMe)(2)Br(4)] complexes. These materials were used as a platform to compare electronic structure and bonding in [U(NR)(2)](2+) with [UO(2)](2+). Specifically, Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT and TDDFT) were used to probe U-Cl bonding interactions in [PPh(4)](2)[U(N(t)Bu)(2)Cl(4)] and [PPh(4)](2)[UO(2)Cl(4)]. The DFT and XAS results show the total amount of Cl 3p character mixed with the U 5f orbitals was roughly 7-10% per U-Cl bond for both compounds, which shows that moving from oxo to imido has little effect on orbital mixing between the U 5f and equatorial Cl 3p orbitals. The results are presented in the context of recent Cl K-edge XAS and DFT studies on other hexavalent uranium chloride systems with fewer oxo or imido ligands.
- Published
- 2013
116. Functional group dependence of the acid catalyzed ring opening of biomass derived furan rings: an experimental and theoretical study
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L. A. 'Pete' Silks, Richard L. Martin, Ruilian Wu, John C. Gordon, Ryan Michael West, Aaron W. Pierpont, Christopher R. Waidmann, and Enrique R. Batista
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chemistry.chemical_classification ,Ketone ,Chemistry ,Protonation ,Ring (chemistry) ,Photochemistry ,Medicinal chemistry ,Catalysis ,Acid catalysis ,chemistry.chemical_compound ,Furan ,Yield (chemistry) ,Reactivity (chemistry) - Abstract
We describe studies of Bronsted acid catalyzed ring opening of substituted furans contained within biomass derived C8- and C9-molecules. Ring opening occurs homogeneously under relatively mild conditions of 80 °C using catalytic hydrochloric acid. In the case of 4-(5-methyl-2-furyl)-2-butanone (1a), the reaction proceeds to a single product in up to 92% yield after 24 hours. For 4-(2-furanyl)-2-butanone (1b) and 4-(5-hydroxymethyl)-2-furanyl-2-butanone (1c), however, multiple products are observed, illustrating the significant influence of furan ring substituents on the reactivity of this class of compounds. The generality of these reaction pathways was tested using several other similar substrates. Kinetics experiments indicate that ring opening of 1a occurs via specific acid catalysis, and computations elucidate the effect of initial protonation on the reaction pathway. Calculated pKa values were calibrated against experimentally measured values and are consistent with observed reactivities. Inclusion of explicit, hydrogen-bonded water molecules in addition to the SMD solvent model is necessary when studying protonation of alcohol and ketone groups.
- Published
- 2013
117. Rotational Rehybridization and the High Temperature Phase of UC2
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Gustavo E. Scuseria, Sven P. Rudin, Xiaodong Wen, David Clark, Enrique R. Batista, and Richard L. Martin
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chemistry.chemical_classification ,Phase transition ,Double bond ,Molecular physics ,Inorganic Chemistry ,Paramagnetism ,Tetragonal crystal system ,Molecular dynamics ,Crystallography ,chemistry ,Phase (matter) ,Density functional theory ,Physical and Theoretical Chemistry ,Open shell - Abstract
The screened hybrid approximation (HSE) of density functional theory (DFT) is used to examine the structural, optical, and electronic properties of the high temperature phase, cubic UC(2). This phase contains C(2) units with a computed C-C distance of 1.443 Å which is in the range of a CC double bond; U is formally 4+, C(2) 4-. The closed shell paramagnetic state (NM) was found to lie lowest. Cubic UC(2) is found to be a semiconductor with a narrow gap, 0.4 eV. Interestingly, the C(2) units connecting two uranium sites can rotate freely up to an angle of 30°, indicating a hindered rotational solid. Ab-initio molecular dynamic simulations (HSE) show that the rotation of C(2) units in the low temperature phase (tetragonal UC(2)) occurs above 2000 K, in good agreement with experiment. The computed energy barrier for the phase transition from tetragonal UC(2) to cubic UC(2) is around 1.30 eV per UC(2). What is fascinating about this system is that at high temperature, the phase transformation to the cubic phase is associated with a rehybridization of the C atoms from sp to sp(3).
- Published
- 2012
118. Spectroscopic and computational investigation of actinium coordination chemistry
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Henry S. La Pierre, Eva R. Birnbaum, Justin N. Cross, Enrique R. Batista, S. Chantal E. Stieber, Juan S. Lezama Pacheco, Justin J. Wilson, Maryline G. Ferrier, Jonathan W. Engle, Stosh A. Kozimor, John M. Berg, and Benjamin W. Stein
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Lanthanide ,Actinium ,Models, Molecular ,Absorption spectroscopy ,Science ,General Physics and Astronomy ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Coordination complex ,Reactivity (chemistry) ,chemistry.chemical_classification ,Radioisotopes ,X-ray absorption spectroscopy ,Multidisciplinary ,Fourier Analysis ,010405 organic chemistry ,General Chemistry ,Actinide ,3. Good health ,0104 chemical sciences ,Solutions ,X-Ray Absorption Spectroscopy ,chemistry ,Physical chemistry ,Density functional theory - Abstract
Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, AcIII reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac–Cl and Ac − O H 2 O distances are measured to be 2.95(3) and 2.59(3) Å, respectively. The X-ray absorption spectroscopy comparisons between AcIII and AmIII in HCl solutions indicate AcIII coordinates more inner-sphere Cl1– ligands (3.2±1.1) than AmIII (0.8±0.3). These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique AcIII chemical behaviour.
- Published
- 2016
119. Extractant Design by Covalency
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Travis S. Grimes, Joe Macor, Andrew J. Gaunt, Angela C. Olson, Dean R. Peterman, Stosh A. Kozimor, Justin N. Cross, and Enrique R. Batista
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X-ray absorption spectroscopy ,Absorption spectroscopy ,Chemistry ,Extraction (chemistry) ,Analytical chemistry ,Physical chemistry ,Density functional theory ,Actinide - Abstract
This project aims to provide an electronic structure-to-function understanding of extractants for actinide selective separation processes. The research entails a multi-disciplinary approach that integrates chemical syntheses, structural determination, K-edge X-ray Absorption Spectroscopy (XAS), and Density Functional Theory (DFT) calculations. In FY15, the project reached the final stage of testing the extraction performance of a new ligand design and preparing an americium-extractant complex for analysis.
- Published
- 2016
120. The MOD-QM/MM Method
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Mikhail Askerka, José A. Gascón, Victor S. Batista, Enrique R. Batista, and Junming Ho
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010304 chemical physics ,Extended X-ray absorption fine structure ,Photosystem II ,Chemistry ,Monte Carlo method ,010402 general chemistry ,Electrostatics ,G-quadruplex ,01 natural sciences ,Quantum chemistry ,Spectral line ,0104 chemical sciences ,QM/MM ,Chemical physics ,Computational chemistry ,0103 physical sciences - Abstract
Quantum mechanics/molecular mechanics (QM/MM) hybrid methods are currently the most powerful computational tools for studies of structure/function relations and catalytic sites embedded in macrobiomolecules (eg, proteins and nucleic acids). QM/MM methodologies are highly efficient since they implement quantum chemistry methods for modeling only the portion of the system involving bond-breaking/forming processes (QM layer), as influenced by the surrounding molecular environment described in terms of molecular mechanics force fields (MM layer). Some of the limitations of QM/MM methods when polarization effects are not explicitly considered include the approximate treatment of electrostatic interactions between QM and MM layers. Here, we review recent advances in the development of computational protocols that allow for rigorous modeling of electrostatic interactions in biomacromolecules and structural refinement, beyond the common limitations of QM/MM hybrid methods. We focus on photosystem II (PSII) with emphasis on the description of the oxygen-evolving complex (OEC) and its high-resolution extended X-ray absorption fine structure spectra (EXAFS) in conjunction with Monte Carlo structural refinement. Furthermore, we review QM/MM structural refinement studies of DNA G4 quadruplexes with embedded monovalent cations and direct comparisons to NMR data.
- Published
- 2016
121. Exploring Electrochemical Windows of Room-Temperature Ionic Liquids: A Computational Study
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Enrique R. Batista, George S. Goff, Yong-Hui Tian, and Wolfgang Runde
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Solvation ,Electrochemistry ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,chemistry ,Chemical physics ,Solvent models ,Ionic liquid ,Materials Chemistry ,Organic chemistry ,Thermal stability ,Physical and Theoretical Chemistry ,Volatility (chemistry) ,Flammability ,Electrochemical window - Abstract
Room-temperature ionic liquids (RTILs) are regarded as green solvents due to their low volatility, low flammability, and thermal stability. RTILs exhibit wide electrochemical windows, making them prime candidates as media for electrochemically driven reactions such as electro-catalysis and electro-plating for separations applications. Therefore, understanding the factors determining edges of the electrochemical window, the electrochemical stability of the RTILs, and the degradation products is crucial to improve the efficiency and applicability of these systems. We present here computational investigations of the electrochemical properties of a variety of RTILs covering a wide range of electrochemical windows. We proposed four different approaches with different degrees of approximation and computational cost from gas-phase calculations to full explicit solvation models. It was found that, whereas the simplest model has significant flaws in accuracy, implicit and explicit solvent models can be used to reliably predict experimental data. The general trend of electrochemical windows of the RTILs studied is well reproduced, showing that it increases in the order of imidazoliumammoniumpyrrolidiniumphosphonium giving confidence to the methodology presented to use it in screening studies of ionic liquids.
- Published
- 2012
122. Sulfur K-edge X-ray Absorption Spectroscopy and Time-Dependent Density Functional Theory of Dithiophosphinate Extractants: Minor Actinide Selectivity and Electronic Structure Correlations
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David Clark, Scott R. Daly, Jason M. Keith, Kevin S. Boland, Stosh A. Kozimor, Richard L. Martin, and Enrique R. Batista
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Lanthanide ,X-ray absorption spectroscopy ,Absorption spectroscopy ,ved/biology ,Chemistry ,ved/biology.organism_classification_rank.species ,Inorganic chemistry ,General Chemistry ,Time-dependent density functional theory ,Biochemistry ,Catalysis ,Spectral line ,Colloid and Surface Chemistry ,K-edge ,Physical chemistry ,Density functional theory ,Conjugate acid - Abstract
The dithiophosphinic acid HS(2)P(o-CF(3)C(6)H(4))(2) is known to exhibit exceptionally high extraction selectivities for trivalent minor actinides (Am and Cm) in the presence of trivalent lanthanides. To generate insight that may account for this observation, a series of [PPh(4)][S(2)PR(2)] complexes, where R = Me (1), Ph (2), p-CF(3)C(6)H(4) (3), m-CF(3)C(6)H(4) (4), o-CF(3)C(6)H(4) (5), o-MeC(6)H(4) (6), and o-MeOC(6)H(4) (7), have been investigated using sulfur K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT). The experimental analyses show distinct features in the spectrum of S(2)P(o-CF(3)C(6)H(4))(2)(-) (5) that are not present in the spectrum of 4, whose conjugate acid exhibits reduced selectivity, or in the spectra of 2 and 3, which are anticipated to have even lower separation factors based on previous studies. In contrast, the spectrum of 5 is similar to those of 6 and 7, despite the significantly different electron-donating properties associated with the o-CF(3), o-Me, and o-OMe substituents. The TDDFT calculations suggest that the distinct spectral features of 5-7 result from steric interactions due to the presence of the ortho substituents, which force the aryl groups to rotate around the P-C bonds and reduce the molecular symmetry from approximately C(2v) in 2-4 to C(2) in 5-7. As a consequence, the change in aryl group orientation appears to make the ortho-substituted S(2)PR(2)(-) anions "softer" extractants compared with analogous Ph-, p-CF(3)C(6)H(4)-, and m-CF(3)C(6)H(4)-containing ligands (2-4) by raising the energies of the sulfur valence orbitals and enhancing orbital mixing between the S(2)P molecular orbitals and the aryl groups bound to phosphorus. Overall, we report that sulfur K-edge XAS experiments and TDDFT calculations reveal unique electronic properties of the S(2)P(o-CF(3)C(6)H(4))(2)(-) anion in 5. These results correlate with the special extraction properties associated with HS(2)P(o-CF(3)C(6)H(4))(2), and suggest that ligand K-edge XAS and TDDFT can be used to guide separation efforts relevant to advanced fuel cycle development.
- Published
- 2012
123. All-Electron Hybrid Density Functional Calculations on UFn and UCln (n = 1-6)
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Gustavo E. Scuseria, Richard L. Martin, Juan E. Peralta, and Enrique R. Batista
- Subjects
Series (mathematics) ,Photoemission spectroscopy ,Computer science ,Operator (physics) ,Electron ,computer.software_genre ,Bond-dissociation energy ,Computer Science Applications ,Molecule ,Data mining ,Physical and Theoretical Chemistry ,Ionization energy ,Atomic physics ,computer - Abstract
We calculate the bond dissociation energies of the series UFn and UCln (n = 1-6) using the all-electron third-order Douglas-Kroll-Hess approximation in combination with hybrid density functionals. The spin-orbit (SO) operator is included self-consistently using the nuclear-only SO and the screened-nuclear SO approximations. Results are in very good agreement with experimental values, with the exception of the smallest molecules of each series, UF and UCl. By shifting the one-electron orbital energies of UF6 and UCl6 to match the HOMO level with the ΔSCF calculated value of the first ionization energy, we are able to reproduce the main features of the photoelectron spectrum of these two molecules.
- Published
- 2015
124. Localization of Electronic Excitations in Conjugated Polymers Studied by DFT
- Author
-
Darryl L. Smith, Iffat Nayyar, Avadh Saxena, Sergei Tretiak, Richard L. Martin, and Enrique R. Batista
- Subjects
Physics ,Condensed matter physics ,Exciton ,Molecule ,General Materials Science ,Density functional theory ,Singlet state ,Physical and Theoretical Chemistry ,Conjugated system ,Solvent effects ,Wave function ,Polaron ,Molecular physics - Abstract
We present an extensive density functional theory (DFT) study on the neutral and charged electronic excitations in oligophenylene vinylenes including lowest singlet (S1) and triplet (T1) excitons and positive (P+) and negative (P−) polarons. We investigated the vibrational and electronic properties of molecules using five different DFT functionals from pure GGA to long-range-corrected hybrids and found an explicit correlation between the spatial extent of the state and the fraction of the orbital exchange. While solvent effects are found to be negligible for neutral (S1 and T1) excitons, they play an important role for charged (P+ and P−) species. S1 states are observed to be spatially less localized compared to the polaronic wave functions (P+ and P−). This is in contrast to the T1 states, which exhibit more spatial confinement in comparison to P+ and P− states.
- Published
- 2011
125. Uranium(VI) bis(imido) disulfonamide and dihalide complexes: Synthesis density functional theory analysis
- Author
-
Ping Yang, James M. Boncella, Brian L. Scott, Enrique R. Batista, and Liam P. Spencer
- Subjects
chemistry.chemical_classification ,Stereochemistry ,General Chemical Engineering ,Iodide ,Ionic bonding ,General Chemistry ,Crystal structure ,Uranyl ,Metathesis ,Medicinal chemistry ,chemistry.chemical_compound ,chemistry ,Amide ,Salt metathesis reaction ,Protonolysis - Abstract
Novel cis- and trans-bis(imido) uranium disulfonamide derivatives have been prepared from iodide metathesis reactions between two equivalents of K[N(Me)(SO2Ar’)] (Ar’ = 4-Me-C6H4) and U(NtBu)2(I)2(L)x (L = OPPh3, x = 2; Me2bpy, x = 1; Me2bpy = 4,4’-dimethyl-2,2’-bipyridyl). These bis(amide) derivatives serve as useful precursors for the synthesis of the trans-diphenolate complex U(NtBu)2(O-2-tBuC6H4)2(OPPh3)2 (5), cis- and trans-dithiolate complexes U(NtBu)2(SPh)2(L)x (L = OPPh3 (6); Me2bpy (7)), and cis- and trans-dihalide complexes with the general formulas U(NtBu)2(X)2(L)x (X = Cl, L = OPPh3 (8), L = Me2bpy (10); X = Br, L = OPPh3 (9), L = Me2bpy (11)). DFT calculations performed on the trans-dihalide series U(NtBu)2(X)2(L)2 and the UO22+ analogues UO2X2(OPPh3)2 suggest that the uranium centers in the [U(NtBu)2]2+ ions possess more covalent character than analogous UO22+ derivatives but that the U-X bonds in the U(NtBu)2X2L2 complexes possess a more ionic nature.
- Published
- 2010
126. Systematic Study of Modifications to Ruthenium(II) Polypyridine Dyads for Electron Injection Enhancement
- Author
-
Enrique R. Batista, Elena Jakubikova, and Richard L. Martin
- Subjects
Ligand ,chemistry.chemical_element ,Bridging ligand ,Chromophore ,Photochemistry ,Ruthenium ,Inorganic Chemistry ,chemistry.chemical_compound ,Bipyridine ,chemistry ,Phenylene ,Covalent bond ,parasitic diseases ,Physical and Theoretical Chemistry ,Terpyridine - Abstract
Spatial localization of excited-state electrons in transition-metal complexes used as photocatalysts or dye sensitizers in solar cells is important for efficient electron injection into the metal oxide nanoparticles. We use density functional theory to investigate the excited states in a prototype catalyst-chromophore assembly [(bpy)(H(2)O)Ru(tpy-tpy)Ru(tpy)](4+) ([Ru(tpy)(bpy)(H(2)O)](2+) = catalyst, [Ru(tpy)(2)](2+) = chromophore, tpy = 2,2':6',2''-terpyridine, and bpy = 2,2'-bipyridine) and a series of related compounds. We explore several bridging ligand and terminal tpy ligand modifications of the prototype assembly, with the aim of inducing electronic excitations into the terminal tpy ligand upon irradiation with visible light. The excitations into the terminal ligand (i.e., ligand covalently attached to the semiconductor in the photocatalytic synthetic cell) should, in turn, enhance electron injection into the semiconductor. Our results suggest that both introduction of a spacer group (such as phenylene or alkane) into the tpy-tpy bridge and replacement of the terminal tpy group by a more extended pi-conjugated ligand are necessary to shift the electronic excitations from the bridging ligand into the terminal ligand. These results have implications for the design of photocatalysts and dye-sensitizer assemblies based on ruthenium(II) terpyridine compounds.
- Published
- 2010
127. Electronic Structure and Spectroscopy of [Ru(tpy)2]2+, [Ru(tpy)(bpy)(H2O)]2+, and [Ru(tpy)(bpy)(Cl)]+
- Author
-
Weizhong Chen, Francisca N. Rein, Richard L. Martin, Dana M. Dattelbaum, Enrique R. Batista, Elena Jakubikova, and Reginaldo C. Rocha
- Subjects
Ligand ,chemistry.chemical_element ,Electronic structure ,Photochemistry ,Polarizable continuum model ,Ruthenium ,Inorganic Chemistry ,Crystallography ,chemistry ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,Solvent effects ,Spectroscopy - Abstract
We use a combined, theoretical and experimental, approach to investigate the spectroscopic properties and electronic structure of three ruthenium polypyridyl complexes, [Ru(tpy)(2)](2+), [Ru(tpy)(bpy)(H(2)O)](2+), and [Ru(tpy)(bpy)(Cl)](+) (tpy = 2,2':6',2''-terpyridine and bpy = 2,2'-bipyridine) in acetone, dichloromethane, and water. All three complexes display strong absorption bands in the visible region corresponding to a metal-to-ligand-charge-transfer (MLCT) transition, as well as the emission bands arising from the lowest lying (3)MLCT state. [Ru(tpy)(bpy)(Cl)](+) undergoes substitution of the Cl(-) ligand by H(2)O in the presence of water. Density functional theory (DFT) calculations demonstrate that the triplet potential energy surfaces of these molecules are complicated, with several metal-centered ((3)MC) and (3)MLCT states very close in energy. Solvent effects are included in the calculations via the polarizable continuum model as well as explicitly, and it is shown that they are critical for proper characterization of the triplet excited states of these complexes.
- Published
- 2009
128. Interfacial Electron Transfer in TiO2 Surfaces Sensitized with Ru(II)−Polypyridine Complexes
- Author
-
Robert C. Snoeberger, Richard L. Martin, Victor S. Batista, Elena Jakubikova, and Enrique R. Batista
- Subjects
Titanium ,Pyridines ,Surface Properties ,Chemistry ,chemistry.chemical_element ,Electrons ,Photochemistry ,Ruthenium ,Photoexcitation ,Bipyridine ,chemistry.chemical_compound ,Electron transfer ,Models, Chemical ,Covalent bond ,Excited state ,Organometallic Compounds ,Quantum Theory ,Computer Simulation ,Density functional theory ,Physical and Theoretical Chemistry ,Terpyridine - Abstract
Studies of interfacial electron transfer (IET) in TiO(2) surfaces functionalized with (1) pyridine-4-phosphonic acid, (2) [Ru(tpy)(tpy(PO(3)H(2)))](2+), and (3) [Ru(tpy)(bpy)(H(2)O)-Ru(tpy)(tpy(PO(3)H(2)))](4+) (tpy = 2,2':6,2''-terpyridine; bpy = 2,2'-bipyridine) are reported. We characterize the electronic excitations, electron injection time scales, and interfacial electron transfer (IET) mechanisms through phosphonate anchoring groups. These are promising alternatives to the classic carboxylates of conventional dye-sensitized solar cells since they bind more strongly to TiO(2) surfaces and form stable covalent bonds that are unaffected by humidity. Density functional theory calculations and quantum dynamics simulations of IET indicate that electron injection in 1-TiO(2) can be up to 1 order of magnitude faster when 1 is attached to TiO(2) in a bidentate mode (tau approximately 60 fs) than when attached in a monodentate motif (tau approximately 460 fs). The IET time scale also depends strongly on the properties of the sensitizer as well as on the nature of the electronic excitation initially localized in the adsorbate molecule. We show that IET triggered by the visible light excitation of 2-TiO(2) takes 1-10 ps when 2 is attached in a bidentate mode, a time comparable to the lifetime of the excited electronic state. IET due to visible-light photoexcitation of 3-TiO(2) is slower, since the resulting electronic excitation remains localized in the tpy-tpy bridge that is weakly coupled to the electronic states of the conduction band of TiO(2). These results are particularly valuable to elucidate the possible origin of IET efficiency drops during photoconversion in solar cells based on Ru(II)-polypyridine complexes covalently attached to TiO(2) thin films with phosphonate linkers.
- Published
- 2009
129. Cation-Cation Interactions, Magnetic Communication, and Reactivity of the Pentavalent Uranium Ion [U(NtBu)2]+
- Author
-
Brian L. Scott, James M. Boncella, Eric J. Schelter, Joe D. Thompson, Robyn L. Gdula, Enrique R. Batista, Ping Yang, Liam P. Spencer, and Jaqueline L. Kiplinger
- Subjects
chemistry.chemical_compound ,Crystallography ,Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Reactivity (chemistry) ,General Chemistry ,Actinide ,Electronic structure ,Uranium ,Imide ,Catalysis ,Ion - Abstract
Communication is important: The dimeric bis(imido) uranium complex [{U(NtBu)(2)(I)(tBu(2)bpy)}(2)] (see picture; U green, N blue, I red) has cation-cation interactions between [U(NR)(2)](+) ions. This f(1)-f(1) system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.
- Published
- 2009
130. Cation-Cation Interactions, Magnetic Communication, and Reactivity of the Pentavalent Uranium Ion [U(NtBu)2]+
- Author
-
Liam P. Spencer, Eric J. Schelter, Ping Yang, Robyn L. Gdula, Brian L. Scott, Joe D. Thompson, Jaqueline L. Kiplinger, Enrique R. Batista, and James M. Boncella
- Subjects
General Medicine - Published
- 2009
131. Synthesis, crystallographic characterization, and conformational prediction of a structurally unique molecular mixed-ligand U(VI) solid, Na6[UO2(O2)2(OH)2](OH)2·14H2O
- Author
-
Ralph A. Zehnder, Shane Peper, Enrique R. Batista, Wolfgang Runde, George S. Goff, and Brian L. Scott
- Subjects
chemistry.chemical_compound ,Crystallography ,chemistry ,Moiety ,Hydroxide ,Density functional theory ,Crystal structure ,Physical and Theoretical Chemistry ,Uranyl ,Peroxide ,Single crystal ,Monoclinic crystal system - Abstract
The first mononuclear molecular mixed-ligand U(VI) solid containing hydroxide and peroxide ligands, Na6[UO2(O2)2(OH)2](OH)2·14H2O (I), was synthesized and structurally characterized using single crystal X-ray diffraction. The crystal structure of I consisted of [UO2(O2)2(OH)2]4− molecular units, with a uranyl(VI) moiety perpendicular to 6 equatorial O atoms belonging to two side-on trans peroxo groups and two terminal trans hydroxo groups. Density functional theory (DFT) calculations determined that the trans -conformer of the [UO2(O2)2(OH)2]4− molecular unit found in I was 24 kcal/mol lower in energy than the previously proposed cis -conformer. Crystal data: monoclinic, space group P21/n with a=13.357(4) Å, b=5.8521(15) Å, c=15.948(6) Å, β=112.292(4)°, and Z=2.
- Published
- 2008
132. Theoretical Studies on the Redox Potentials of Fe Dinuclear Complexes as Models for Hydrogenase
- Author
-
Lindsay E. Roy, P. Jeffrey Hay, and Enrique R. Batista
- Subjects
Models, Molecular ,Hydrogenase ,Chemistry ,Ligand ,Iron ,Spectrochemical series ,Molecular Conformation ,Solvation ,Electrons ,Redox ,Inorganic Chemistry ,chemistry.chemical_compound ,Models, Chemical ,Atomic orbital ,Computational chemistry ,Solvents ,Quantum Theory ,Physical and Theoretical Chemistry ,Acetonitrile ,Oxidation-Reduction ,Mulliken population analysis - Abstract
Density Functional calculations have been performed at the uB3LYP and uBP86 levels to calculate the one-electron redox potentials for a series of small models based on the diiron hydrogenase enzymes in the presence of acetonitrile (MeCN). The solvation effects in MeCN are incorporated via a self-consistent reaction field (SCRF) using the polarized continuum model (PCM). The calculated redox potentials reproduce the trends in experimental data with an average error of only 0.12 V using the BP86 functional, whereas comparing results with the B3LYP functional require a systematic shift of -0.82 and -0.53 V for oxidation and reduction, respectively. The bonding orbitals and d-electron populations were examined using Mulliken population analysis, and the results were used to rationalize the calculated and observed redox potentials. These studies demonstrate that the redox potential correlates with the empirical spectrochemical series for the ligands, as well as with the amount of electron density donated by the ligand onto the Fe centers.
- Published
- 2008
133. Electronic Structure of Self-Assembled Amorphous Polyfluorenes
- Author
-
Ping Yang, Darryl L. Smith, Richard L. Martin, Avadh Saxena, Sergei Tretiak, Enrique R. Batista, and Svetlana Kilina
- Subjects
Models, Molecular ,Materials science ,Macromolecular Substances ,Surface Properties ,Band gap ,Molecular Conformation ,General Physics and Astronomy ,Electronic structure ,Molecular dynamics ,Computational chemistry ,Nanotechnology ,Computer Simulation ,General Materials Science ,Particle Size ,Titanium ,Fluorenes ,Quantitative Biology::Biomolecules ,Intermolecular force ,Electric Conductivity ,General Engineering ,Nanostructures ,Amorphous solid ,Condensed Matter::Soft Condensed Matter ,Molecular geometry ,Models, Chemical ,Semiconductors ,Chemical physics ,Intramolecular force ,Density functional theory ,Crystallization - Abstract
We investigate the role of conformational disorder and intermolecular interactions on the electronic structure of amorphous clusters of polyfluorenes. Classical molecular dynamics simulations are used to determine probable molecular geometries and chain packing, and first-principles density functional theory calculations are employed to determine electronic structure and orbital localization properties. Intramolecular and intermolecular effects are disentangled by contrasting results for densely packed oligomer clusters and for ensembles of isolated oligomers with the same intramolecular geometries. Our simulations show that intermolecular disorder allows for nearly planar configurations of interacting fluorenes compared to the isolated molecules. This rationalizes the experimentally detected formation of the planar crystalline morphologies that frequently accompany twisted glassy configurations in fluorene films. The energy gap (HOMO-LUMO gap) significantly decreases for planar configurations. The electron and hole orbital energies are strongly dependent on both torsional angles and intermolecular interactions. This leads to strong localization of electronic states in amorphous polymer aggregates, which is analyzed by examining the respective orbital participation ratios. Notably, the energies of unoccupied levels show stronger dependence on the conformational disorder, compared to that of occupied levels. This results in the more probable formation of trap states near the edge of the conduction band than near the valence band.
- Published
- 2008
134. Covalency Trends in Group IV Metallocene Dichlorides. Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory
- Author
-
Carol J. Burns, Juan S. Lezama, Kevin S. Boland, Daniel E. Schwarz, Stosh A. Kozimor, Christin N. Christensen, Richard L. Martin, P. Jeffrey Hay, Laura E. Wolfsberg, Marianne P. Wilkerson, David Clark, Steven D. Conradson, Ping Yang, and Enrique R. Batista
- Subjects
X-ray absorption spectroscopy ,X-ray spectroscopy ,Absorption spectroscopy ,Chemistry ,Inorganic chemistry ,Time-dependent density functional theory ,Ion ,Inorganic Chemistry ,Crystallography ,chemistry.chemical_compound ,K-edge ,Physical and Theoretical Chemistry ,Metallocene ,Group 2 organometallic chemistry - Abstract
For 3-5d transition-metal ions, the (C5R5)2MCl2 (R = H, Me for M = Ti, Zr, Hf) bent metallocenes represent a series of compounds that have been central in the development of organometallic chemistry and homogeneous catalysis. Here, we evaluate how changes in the principal quantum number for the group IV (C5H5)2MCl2 (M = Ti, Zr, Hf; 1- 3, respectively) complexes affects the covalency of M-Cl bonds through application of Cl K-edge X-ray Absorption Spectroscopy (XAS). Spectra were recorded on solid samples dispersed as a thin film and encapsulated in polystyrene matrices to reliably minimize problems associated with X-ray self-absorption. The data show that XAS pre-edge intensities can be quantitatively reproduced when analytes are encapsulated in polystyrene. Cl K-edge XAS data show that covalency in M-Cl bonding changes in the order TiZrHf and demonstrates that covalency slightly decreases with increasing principal quantum number in 1-3. The percent Cl 3p character was experimentally determined to be 26, 23, and 18% per M-Cl bond in the thin-film samples for 1-3 respectively and was indistinguishable from the polystyrene samples, which analyzed as 25, 25, and 19% for 1-3, respectively. To aid in interpretation of Cl K-edge XAS, 1-3 were also analyzed by ground-state and time-dependent density functional theory (TD-DFT) calculations. The calculated spectra and percent chlorine character are in close agreement with the experimental observations, and show 20, 18, and 17% Cl 3p character per M-Cl bond for 1-3, respectively. Polystyrene matrix encapsulation affords a convenient method to safely contain radioactive samples to extend our studies to include actinide elements, where both 5f and 6d orbitals are expected to play a role in M-Cl bonding and where transition assignments must rely on accurate theoretical calculations.
- Published
- 2008
135. Effect of Packing on Formation of Deep Carrier Traps in Amorphous Conjugated Polymers
- Author
-
Richard L. Martin, Enrique R. Batista, Sergei Tretiak, Avadh Saxena, Naveen Dandu, Darryl L. Smith, and Svetlana Kilina
- Subjects
chemistry.chemical_classification ,Intermolecular force ,Amorphous solid ,Delocalized electron ,Molecular dynamics ,chemistry ,Chemical physics ,Side chain ,Organic chemistry ,General Materials Science ,Molecular orbital ,Density functional theory ,Physical and Theoretical Chemistry ,Alkyl - Abstract
We theoretically investigate the role of conformational disorder and intermolecular interactions on the localization properties of electronic states, leading to the formation of carrier traps in amorphous aggregates of conjugated polymers. Samples of amorphous conformations of poly(p-phenylene vinylene) (PPV), poly2-methoxy-5-(2-ethyl-hexyloxy)PPV (MEH-PPV), and [poly-(9,9'-dioctyluorene)] (PFO) oligomers are simulated by classical molecular dynamics, while their electronic structure is calculated using first-principles density functional theory. Localization and delocalization properties of molecular orbitals are studied based on the participation ratio analysis, an approach commonly used in inorganic semiconductors. Our simulations confirm that the alkyl side chains insignificantly affect the conformational disorder in amorphous polymers while having a dramatic effect on the intermolecular disorder and packing. The nature of the disorder and its impact on charge-carrier localization in amorphous polymers with alkyl side chains differ drastically from those of disordered polymers without side chains, such as PPVs. Thus, long-range intermolecular interactions and sparse packing are responsible for the formation of multiple, deep, highly localized trap states in amorphous MEH-PPVs and PFOs, while close packing in combination with conformational disorder leads to the trap states distributed mostly near the bandgap edges in PPV aggregates.
- Published
- 2015
136. A Linear trans-Bis(imido) Neptunium(V) Actinyl Analog: Np(V)(NDipp)2((t)Bu2bipy)2Cl (Dipp = 2,6-(i)Pr2C6H3)
- Author
-
Neil C. Tomson, Jessie L. Brown, James M. Boncella, Brian L. Scott, Enrique R. Batista, Sean D. Reilly, and Andrew J. Gaunt
- Subjects
Neptunium ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Electronic structure ,Uranium ,Biochemistry ,Catalysis ,Bipyridine ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Reagent ,Proton NMR ,Transuranium element - Abstract
The discovery that imido analogs of actinyl dioxo cations can be extended beyond uranium into the transuranic elements is presented. Synthesis of the Np(V) complex, Np(NDipp)2((t)Bu2bipy)2Cl (1), is achieved through treatment of a Np(IV) precursor with a bipyridine coligand and lithium-amide reagent. Complex 1 has been structurally characterized, analyzed by (1)H NMR and UV-vis-NIR spectroscopies, and the electronic structure evaluated by DFT calculations.
- Published
- 2015
137. Computational Studies of Bonding and Reactivity in Actinide Molecular Complexes
- Author
-
Richard L. Martin, Enrique R. Batista, and Ping Yang
- Subjects
Computational chemistry ,Chemistry ,Inorganic chemistry ,Reactivity (chemistry) ,Actinide - Published
- 2015
138. Using Solution- and Solid-State S K-edge X-ray Absorption Spectroscopy with Density Functional Theory to Evaluate M–S Bonding for MS42- (M = Cr, Mo, W) Dianions
- Author
-
Scott R. Daly, Jason M. Keith, Kevin S. Boland, Richard L. Martin, Enrique R. Batista, Molly M. MacInnes, Angela C. Olson, Stosh A. Kozimor, and Brian L. Scott
- Subjects
Anions ,Chromium ,Molybdenum ,X-ray absorption spectroscopy ,Valence (chemistry) ,Absorption spectroscopy ,Chemistry ,Time-dependent density functional theory ,Electronic structure ,Article ,Tungsten ,Inorganic Chemistry ,Solutions ,X-Ray Absorption Spectroscopy ,Atomic orbital ,Principal quantum number ,Physical chemistry ,Quantum Theory ,Density functional theory ,Atomic physics - Abstract
Herein, we have evaluated relative changes in M-S electronic structure and orbital mixing in Group 6 MS4(2-) dianions using solid- and solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well as density functional theory (DFT; M = Cr, Mo, W) and time-dependent density functional theory (TDDFT) calculations. To facilitate comparison with solution measurements (conducted in acetonitrile), theoretical models included gas-phase calculations as well as those that incorporated an acetonitrile dielectric, the latter of which provided better agreement with experiment. Two pre-edge features arising from S 1s → e* and t electron excitations were observed in the S K-edge XAS spectra and were reasonably assigned as (1)A1 → (1)T2 transitions. For MoS4(2-), both solution-phase pre-edge peak intensities were consistent with results from the solid-state spectra. For WS4(2-), solution- and solid-state pre-edge peak intensities for transitions involving e* were equivalent, while transitions involving the t orbitals were less intense in solution. Experimental and computational results have been presented in comparison to recent analyses of MO4(2-) dianions, which allowed M-S and M-O orbital mixing to be evaluated as the principle quantum number (n) for the metal valence d orbitals increased (3d, 4d, 5d). Overall, the M-E (E = O, S) analyses revealed distinct trends in orbital mixing. For example, as the Group 6 triad was descended, e* (π*) orbital mixing remained constant in the M-S bonds, but increased appreciably for M-O interactions. For the t orbitals (σ* + π*), mixing decreased slightly for M-S bonding and increased only slightly for the M-O interactions. These results suggested that the metal and ligand valence orbital energies and radial extensions delicately influenced the orbital compositions for isoelectronic ME4(2-) (E = O, S) dianions.
- Published
- 2014
139. A Self-Consistent Space-Domain Decomposition Method for QM/MM Computations of Protein Electrostatic Potentials
- Author
-
Victor S. Batista, Siegfried S. F. Leung, Enrique R. Batista, and José A. Gascón
- Subjects
Quantitative Biology::Biomolecules ,Chemistry ,Computation ,Domain decomposition methods ,Self consistent ,Space (mathematics) ,Electrostatics ,Molecular physics ,Computer Science Applications ,QM/MM ,Iterated function ,Quantum mechanics ,Physical and Theoretical Chemistry ,Polarization (electrochemistry) - Abstract
This paper introduces a self-consistent computational protocol for modeling protein electrostatic potentials according to static point-charge model distributions. The protocol involves a simple space-domain decomposition scheme where individual molecular domains are modeled as Quantum-Mechanical (QM) layers embedded in the otherwise classical Molecular-Mechanics (MM) protein environment. ElectroStatic-Potential (ESP) atomic charges of the constituent molecular domains are computed, to account for mutual polarization effects, and iterated until obtaining a self-consistent point-charge model of the protein electrostatic potential. The novel protocol achieves quantitative agreement with full QM calculations in the description of electrostatic potentials of small polypeptides where polarization effects are significant, showing a remarkable improvement relative to the corresponding electrostatic potentials obtained with popular MM force fields. The capabilities of the method are demonstrated in several applications, including calculations of the electrostatic potential in the potassium channel protein and the description of protein-protein electrostatic interactions.
- Published
- 2005
140. On the Excited States Involved in the Luminescent Probe [Ru(bpy)2dppz]2+
- Author
-
Richard L. Martin and Enrique R. Batista
- Subjects
Dark state ,Chemistry ,Excited state ,Molecule ,chemistry.chemical_element ,Density functional theory ,Time-dependent density functional theory ,Physical and Theoretical Chemistry ,Solvent effects ,Atomic physics ,Ruthenium ,Hybrid functional - Abstract
The nature of the excited states of [Ru(bpy) 2 dppz] 2 + has been investigated using density functional theory with the hybrid functional B3LYP. The excitations were studied via linear response theory (TDDFT) and ΔSCF calculations and the solvent effects were introduced by embedding the molecule in a continuum dielectric medium. It was found that the solvent effects are critical in understanding the nature of the excitations. For the molecule in ethanol, the lowest absorption predicted by TDDFT is a dark state 3 π → π* with the electron and hole spread over the dppz ligand. Next come the excitations of 3 MLCT between the ruthenium and the dppz and finally the 3 MLCT excitations between the ruthenium and the bpy ligands not associated with the phenazine. Using ΔSCF calculations two low-lying excited states were identified and the geometry optimized in the presence of the continuum medium. At the optimal geometry the lowest excited state is 3 MLCT (Ru → dppz). The 3 π → π* state is found only 0.026 eV higher.
- Published
- 2005
141. Scanning Tunneling Microscopy and Theoretical Study of Competitive Reactions in the Dissociative Chemisorption of CCl4 on Iron Oxide Surfaces
- Author
-
Richard M. Osgood, George W. Flynn, Thomas Müller, S. A. Joyce, Enrique R. Batista, Kwang Taeg Rim, Jeffrey P. Fitts, Richard A. Friesner, Nicholas Camillone, and Kaveh Adib
- Subjects
Ab initio ,Iron oxide ,chemistry.chemical_element ,Surfaces, Coatings and Films ,law.invention ,chemistry.chemical_compound ,chemistry ,Computational chemistry ,Chemisorption ,law ,Atom ,Materials Chemistry ,Chlorine ,Molecule ,Physical chemistry ,Physical and Theoretical Chemistry ,Phosgene ,Scanning tunneling microscope - Abstract
Variable temperature scanning tunneling microscopy (VT STM) and theoretical ab initio computer simulations were used to study dissociative chemisorption and competitive surface chemistry of CCl 4 on an iron-terminated Fe 3 O 4 (111) 2 × 2 surface in an ultrahigh vacuum. The Fe 3 O 4 (111) surface was exposed to CCl 4 molecules at 224 K, slowly annealed to 500 K (0.2 K/s), and scanned at room temperature. Two different chlorine species were observed only on the iron-terminated Fe 3 O 4 (111) 2 × 2 surface due to chemisorption of CCl 4 , one on top of surface-terminating iron atoms (Cl bound to surface irons) and the other at 3-fold oxygen vacancy sites (Cl bound to subsurface irons). The ratio of the number of chlorine species on top sites to the number at 3-fold oxygen vacancy sites is approximately 9:1, which is dramatically different from the 1:10 ratio observed when CCl 4 is dosed at room temperature. The difference in the ratio of these two chlorine species can be explained with a competitive surface reaction picture in which phosgene evolution/surface oxygen atom abstraction, leading to chlorine species at 3-fold oxygen vacancy sites, can only favorably compete with recombination and association reactions, leading to chlorine atoms on top sites, near room temperature. Theoretical calculations were performed that predict an activation barrier of 0.16 eV for the production of phosgene from CCl 4 reacting with the iron-terminated Fe 3 O 4 (111) 2 x 2 surface.
- Published
- 2004
142. Density functional investigations of the properties and thermochemistry of UF6 and UF5 using valence-electron and all-electron approaches
- Author
-
Gustavo E. Scuseria, Richard L. Martin, Juan E. Peralta, P. Jeffrey Hay, and Enrique R. Batista
- Subjects
Chemistry ,General Physics and Astronomy ,Electron ,Bond-dissociation energy ,Hybrid functional ,symbols.namesake ,Chemical thermodynamics ,Thermochemistry ,symbols ,Density functional theory ,Physical and Theoretical Chemistry ,Atomic physics ,Hamiltonian (quantum mechanics) ,Valence electron - Abstract
The structural properties and thermochemistry of UF6 and UF5 have been investigated using both Hartree-Fock and density functional theory (DFT) approximations. Within the latter approach, the local spin-density approximation, the generalized gradient approximation, and hybrid density functionals were considered. To describe the uranium atom we employed small-core (60 electrons) and large-core (78 electrons) relativistic effective core potentials (RECPs), as well as the all-electron approximation based on the two-component third-order Douglas-Kroll-Hess Hamiltonian. For structural properties, we obtained very good agreement with experiment with DFT and both large and small-core RECPs. The best match with experiment is given by the hybrid functionals with the small-core RECP. The bond dissociation energy (BDE) was obtained from the relative energies of the fragments [UF6 --> UF5 + F], corrected for zero-point energy and spin-orbit interaction. Very good agreement was found between the BDE obtained from all-electron calculations and those calculated with the small-core RECP, while those from the large-core RECP are off by more than 50%. In order to obtain good agreement with experiment in the BDE it is imperative to work with hybrid density functionals and a small-core RECP.
- Published
- 2004
143. A Self-Consistent Charge-Embedding Methodology for ab Initio Quantum Chemical Cluster Modeling of Ionic Solids and Surfaces: Application to the (001) Surface of Hematite (α-Fe2O3)
- Author
-
Richard A. Friesner and Enrique R. Batista
- Subjects
Coupled cluster ,Field (physics) ,Chemistry ,Point particle ,Materials Chemistry ,Ab initio ,Cluster (physics) ,Quantum simulator ,Electronic structure ,Physical and Theoretical Chemistry ,Atomic physics ,Electrostatics ,Surfaces, Coatings and Films - Abstract
To ab initio simulate an ionic crystal using a cluster of atoms, one must surround that cluster with point charges. These point charges add the effect of the electrostatic potential of the rest of the crystal on the electronic structure of the quantum cluster. The value of the point charges has to be chosen to reproduce the crystal field in the region of the cluster. In this work, a method to compute the necessary point charges is presented. The algorithm to choose the point charges is an extension of the one presented by Derenzo et al. [J. Chem. Phys. 2000, 112, 2074]. The method consists of a self-consistent loop, fitting in each iteration the value of the point charges to reproduce the electrostatic field, calculated from the quantum simulation, in the region of the cluster. This method was then applied to the study of the (001) basal surface of hematite, α-Fe2O3. As the cluster size is systematically increased, it is shown that to fully converge the electrostatic effect on the electronic structure of ...
- Published
- 2002
144. Insights on uranium halogen bonding derived from charge-density studies at 20 K
- Author
-
Stefan G. Minasian, A. Alan Pinkerton, Enrique R. Batista, Christian Jelsch, Christopher G. Gianopoulos, and Vladimir V. Zhurov
- Subjects
Inorganic Chemistry ,Halogen bond ,Materials science ,chemistry ,Structural Biology ,Physical chemistry ,Charge density ,chemistry.chemical_element ,General Materials Science ,Physical and Theoretical Chemistry ,Uranium ,Condensed Matter Physics ,Biochemistry - Published
- 2017
145. Diffusion and Island formation on the ice Ih basal plane surface
- Author
-
Enrique R. Batista and Hannes Jónsson
- Subjects
Surface diffusion ,Arrhenius equation ,General Computer Science ,Chemistry ,Binding energy ,General Physics and Astronomy ,Ice Ih ,General Chemistry ,Activation energy ,Thermal diffusivity ,Kinetic energy ,Molecular physics ,Mean squared displacement ,Computational Mathematics ,Crystallography ,symbols.namesake ,Mechanics of Materials ,symbols ,General Materials Science - Abstract
We present theoretical calculations of the adsorption, diffusion and island formation of water admolecules on the basal plane surface of an ice Ih crystal. These are preliminary calculations based on the simple TIP4P interaction potential, a pairwise additive potential function based on point charges. At low coverage, we find that an admolecule prefers to sit at non-crystallographic sites on the surface (i.e., sites that do not fit into the ice lattice). Since ice Ih is proton disordered, no two sites are exactly the same and there is a wide range of binding energies. For some local environments the binding energy is of the order of, or even larger than, the cohesive energy. The proton disorder also results in a range of activation energies for diffusion. After mapping out a large number of diffusion barriers using the nudged elastic band method, a kinetic Monte-Carlo calculation of the diffusion at 140 K was performed. At early time, the mean squared displacement has anomalous scaling with time as is common for diffusion on random lattices. But, at longer time the scaling is normal and a diffusion coefficient can be obtained. The diffusivity is slightly larger than a recent experimental upper bound given by Brown and George. The energetics and dynamics of the formation of small islands on the ice surface have also been studied. It is found that islands up to and including pentamer are non-crystallographic, but the hexamer is crystallographic. While the formation of a crystallographic hexamer from a non-crystallographic pentamer and a new admolecule involves a complex concerted motion of all the island molecules and a large relaxation of the substrate, the activation energy for the process is estimated to be quite small, smaller than the admolecule diffusion barrier.
- Published
- 2001
146. Kinetics of alkali-based photocathode degradation
- Author
-
Nathan A. Moody, Fangze Liu, Mark A. Hoffbauer, Enrique R. Batista, and Vitaly Pavlenko
- Subjects
010302 applied physics ,Langmuir ,Chemistry ,Analytical chemistry ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Chemical reaction ,lcsh:QC1-999 ,Photocathode ,Adsorption ,Physisorption ,Desorption ,0103 physical sciences ,Degradation (geology) ,Chemical change ,0210 nano-technology ,lcsh:Physics - Abstract
We report on a kinetic model that describes the degradation of the quantum efficiency (QE) of Cs3Sb and negative electron affinity (NEA) GaAs photocathodes under UHV conditions. In addition to the generally accepted irreversible chemical change of a photocathode’s surface due to reactions with residual gases, such as O2, CO2, and H2O, the model incorporates an intermediate reversible physisorption step, similar to Langmuir adsorption. This intermediate step is needed to satisfactorily describe the strongly non-exponential QE degradation curves for two distinctly different classes of photocathodes –surface-activated and “bulk,” indicating that in both systems the QE degradation results from surface damage. The recovery of the QE upon improvement of vacuum conditions is also accurately predicted by this model with three parameters (rates of gas adsorption, desorption, and irreversible chemical reaction with the surface) comprising metrics to better characterize the lifetime of the cathodes, instead of time-pressure exposure expressed in Langmuir units.
- Published
- 2016
147. Electric fields in ice and near water clusters
- Author
-
Sotiris S. Xantheas, Enrique R. Batista, and Hannes Jónsson
- Subjects
Dipole ,Magnetic moment ,Chemistry ,Polarizability ,Electric field ,Quadrupole ,Moment (physics) ,Physics::Atomic and Molecular Clusters ,General Physics and Astronomy ,Ice Ih ,Physical and Theoretical Chemistry ,Atomic physics ,Multipole expansion - Abstract
We have studied the electric field near water clusters and in ice Ih using first principles calculations. We employed Mo/ller–Plesset perturbation theory (MP2) for the calculations of the clusters up to and including the hexamer, and density functional theory (DFT) with a gradient dependent functional [Perdew–Wang (PW91)] for ice Ih as well as the clusters. The electric field obtained from the first principles calculations was used to test the predictions of an induction model based on single center multipole moments and polarizabilities of an isolated water molecule. We found that the fields obtained from the induction model agree well with the first principles results when the multipole expansion is carried out up to and including the hexadecapole moment, and when polarizable dipole and quadrupole moments are included. This implies that accurate empirical water interaction potential functions transferable to various environments such as water clusters and ice surfaces could be based on a single center m...
- Published
- 2000
148. Elastic sheet method for identifying atoms in molecules
- Author
-
Enrique R. Batista, Blas P. Uberuaga, and Hannes Jónsson
- Subjects
Surface (mathematics) ,Crystal ,Electron density ,Uniform distribution (continuous) ,Classical mechanics ,Chemistry ,Component (thermodynamics) ,Atoms in molecules ,Convergence (routing) ,Tangent space ,General Physics and Astronomy ,Geometry ,Physical and Theoretical Chemistry - Abstract
We have developed a new method for finding and representing dividing surfaces which can, for example, be used to identify “atoms” in molecules or condensed phases based on Bader’s definition. Given the total electron density of the system, the dividing surface is taken to be the zero-flux surface, i.e., the surface on which the normal component of the gradient vanishes. Our method for finding this surface involves creating an “elastic sheet” represented by a swarm of fictitious particles which interact with each other so as to give a nearly uniform distribution of points on the sheet. Two kinds of forces act on the particles: (1) the component of the gradient of the density normal to the elastic sheet, and (2) an interparticle force which only acts in the local tangent plane of the sheet. Starting with a spherical surface and applying an optimization algorithm that minimizes the forces leads to convergence of the particles to the zero-flux surface. The elastic sheet tends to round off regions where the zero-flux surface has sharp cusps or points, but this appears not to be a serious problem in cases we have studied. The elastic sheet method is robust and can converge in situations where currently used methods fail. We demonstrate the method with a study of water clusters and a Si interstitial in a Si crystal.
- Published
- 1999
149. Multipole moments of water molecules in clusters and ice Ih from first principles calculations
- Author
-
Sotiris S. Xantheas, Hannes Jónsson, and Enrique R. Batista
- Subjects
Bond dipole moment ,Dipole ,Chemistry ,Polarizability ,Chemical polarity ,Transition dipole moment ,General Physics and Astronomy ,Ice Ih ,Physics::Atomic Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Multipole expansion ,Magnetic dipole - Abstract
We have calculated molecular multipole moments for water molecules in clusters and in ice Ih by partitioning the charge density obtained from first principles calculations. Various schemes for dividing the electronic charge density among the water molecules were used. They include Bader’s zero flux surfaces and Voronoi partitioning schemes. A comparison was also made with an induction model including dipole, dipole-quadrupole, quadrupole-quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments. We have found that the different density partitioning schemes lead to widely different values for the molecular multipoles, illustrating how poorly defined molecular multipoles are in clusters and condensed environments. For instance, the magnitude of the molecular dipole moment in ice Ih ranges between 2.3 D and 3.1 D depending on the partitioning scheme used. Within each scheme, though, the value for the molecular dipole moment in ice is larger than in the hexamer. The magnitude of the molecular dipole moment in the clusters shows a monotonic increase from the gas phase value to the one in ice Ih, with the molecular dipole moment in the water ring hexamer being smaller than the one in ice Ih for all the partitioning schemes used.
- Published
- 1999
150. Molecular multipole moments of water molecules in ice Ih
- Author
-
Enrique R. Batista, Hannes Jónsson, and Sotiris S. Xantheas
- Subjects
Dipole ,Polarizability ,Chemistry ,Electric field ,Moment (physics) ,General Physics and Astronomy ,Hyperpolarizability ,Ice Ih ,Physics::Atomic Physics ,Water cluster ,Physical and Theoretical Chemistry ,Atomic physics ,Multipole expansion - Abstract
We have used an induction model including dipole, dipole–quadrupole, quadrupole–quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments to study the electric field in ice. The self-consistent induction calculations gave an average total dipole moment of 3.09 D, a 67% increase over the dipole moment of an isolated water molecule. A previous, more approximate induction model study by Coulson and Eisenberg [Proc. R. Soc. Lond. A 291, 445 (1966)] suggested a significantly smaller average value of 2.6 D. This value has been used extensively in recent years as a reference point in the development of various polarizable interaction potentials for water as well as for assessment of the convergence of water cluster properties to those of bulk. The reason for this difference is not due to approximations made in the computational scheme of Coulson and Eisenberg but rather due to the use of less accurate values for the molecular multipoles in these earlier calculations.
- Published
- 1998
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