28 results on '"Visscher, Lucas"'
Search Results
2. A Resolution of Identity Technique to Speed up TDDFT with Hybrid Functionals: Implementation and Application to the Magic Cluster Series Au8n+4(SC6H5)4n+8 (n = 3–6).
- Author
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D'Antoni, Pierpaolo, Medves, Marco, Toffoli, Daniele, Fortunelli, Alessandro, Stener, Mauro, and Visscher, Lucas
- Published
- 2023
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3. Two-component $GW$ calculations: Cubic scaling implementation and comparison of vertex corrected and partially self-consistent $GW$ variants
- Author
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Förster, Arno, van Lenthe, Erik, Spadetto, Edoardo, and Visscher, Lucas
- Subjects
Chemical Physics (physics.chem-ph) ,Physics - Chemical Physics ,FOS: Physical sciences - Abstract
We report an all-electron, atomic orbital (AO) based, two-component (2C) implementation of the $GW$ approximation (GWA) for closed-shell molecules. Our algorithm is based on the space-time formulation of the GWA and uses analytical continuation of the self-energy, and pair-atomic density fitting (PADF) to switch between AO and auxiliary basis. By calculating the dynamical contribution to the $GW$ self-energy at a quasi-one-component level, our 2C $GW$ algorithm is only about a factor of two to three slower than in the scalar relativistic case. Additionally, we present a 2C implementation of the simplest vertex correction to the self-energy, the statically screened $G3W2$ correction. Comparison of first ionization potentials of a set of 67 molecules with heavy elements (a subset of the SOC81 set) calculated with our implementation against results from the WEST code reveals mean absolute deviations of around 70 meV for $G_0W_0$@PBE and $G_0W_0$@PBE0. These are most likely due to technical differences in both implementations, most notably the use of different basis sets, pseudopotential approximations, different treatment of the frequency dependency of the self-energy and the choice of the 2C-Hamiltonian. Finally, we assess the performance of some (partially self-consistent) variants of the GWA for the calculation of first IPs by comparison to vertical experimental reference values. $G_0W_0$PBE0 (25 \% exact exchange) and $G_0W_0$BHLYP (50 \% exact exchange) perform best with mean absolute deviations (MAD) of about 200 meV. Eigenvalue-only self-consistent $GW$ (ev$GW$) and quasi-particle self-consistent $GW$ (qs$GW$) significantly overestimate the IPs. Perturbative $G3W2$ corrections improve the agreement with experiment in cases where $G_0W_0$ alone underestimates the IPs. With a MAD of only 140 meV, 2C-$G_0W_0$PBE0 + $G3W2$ is in best agreement with the experimental reference values., Version with recalculated results due to a bug in the code with which the original results where produced
- Published
- 2023
4. Exploring the Statically Screened $G3W2$ Correction to the $GW$ Self-Energy: Charged Excitations and Total Energies of Finite Systems
- Author
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Förster, Arno, Visscher, Lucas, Theoretical Chemistry, and AIMMS
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Chemical Physics (physics.chem-ph) ,Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Physics - Chemical Physics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Electron correlation in finite and extended systems is often described in an effective single-particle framework within the $GW$ approximation. Here, we use the statically screened second-order exchange contribution to the self-energy ($G3W2$) to calculate a perturbative correction to the $GW$ self-energy. We use this correction to calculate total correlation energies of atoms, relative energies, as well as charged excitations of a wide range of molecular systems. We show that the second-order correction improves correlation energies with respect to the RPA and also improves relative energies for many, but not all considered systems. While the full $G3W2$ contribution does not give consistent improvements over $GW$, taking the average of $GW$ and $GW + G3W2$ generally gives excellent results. Improvements over quasiparticle self-consistent $GW$, which we show to give very accurate charged excitations in small and medium molecules by itself, are only minor. $G_0W_0$ quasiparticle energies evaluated with eigenvalue and orbitals from range-separated hybrids, however, are tremendously improved upon: The second-order corrected $G_0W_0$ outperforms all existing $GW$ methods for the systems considered herein and also does not come with substantially increased computational cost compared to $G_0W_0$ for systems with up to 100 atoms., Revised version as accepted by Physical review B (Phys. Rev. B 2022, 105, 125121, 10.1103/PhysRevB.105.125121) Compared to our first submission, a programming mistake in our first implementation has been corrected leading to different (better) results
- Published
- 2021
5. The DIRAC code for relativistic molecular calculations:The Journal of Chemical Physics
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Saue, Trond, Bast, Radovan, Gomes, André Severo Pereira, Jensen, Hans Jørgen Aa., Visscher, Lucas, Aucar, Ignacio Agustín, Di Remigio, Roberto, Dyall, Kenneth G., Eliav, Ephraim, Fasshauer, Elke, Fleig, Timo, Halbert, Loïc, Hedegård, Erik Donovan, Helmich-Paris, Benjamin, Iliaš, Miroslav, Jacob, Christoph R., Knecht, Stefan, Laerdahl, Jon K., Vidal, Marta L., Nayak, Malaya K., Olejniczak, Małgorzata, Olsen, Jógvan Magnus Haugaard, Pernpointner, Markus, Senjean, Bruno, Shee, Avijit, Sunaga, Ayaki, and van Stralen, Joost N. P.
- Subjects
Physics::Chemical Physics - Abstract
DIRAC is a freely distributed general-purpose program system for one-, two-, and four-component relativistic molecular calculations at the level of Hartree–Fock, Kohn–Sham (including range-separated theory), multiconfigurational self-consistent-field, multireference configuration interaction, electron propagator, and various flavors of coupled cluster theory. At the self-consistent-field level, a highly original scheme, based on quaternion algebra, is implemented for the treatment of both spatial and time reversal symmetry. DIRAC features a very general module for the calculation of molecular properties that to a large extent may be defined by the user and further analyzed through a powerful visualization module. It allows for the inclusion of environmental effects through three different classes of increasingly sophisticated embedding approaches: the implicit solvation polarizable continuum model, the explicit polarizable embedding model, and the frozen density embedding model.
- Published
- 2020
6. Quantum Chemical Workflow Automation to facilitate computational chemistry calculations
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Zapata, Felipe, Ridder, Lars, Hidding, Johan, Gangarapu, Satesh, Infante, Ivan, and Visscher, Lucas
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Quantum Chemistry python automation workflows - Abstract
Modern research based on computational quantum chemistry typically involves various types of interdependent calculations, on series of molecular systems and/or conformations and are performed with different computational chemistry software. Such extensive computational studies require great effort by the researcher to prepare, submit, run and analyze the simulations and is usually done through shell scripts that try to automate these tasks. Such scripts are difficult to maintain and extend, requiring a significant programming expertise to work with them. In this communication we present a workflow solution under development that aims to: automate input generation, job distribution, failure detection and recovery, dependency resolution, etc. We also present the preliminary results obtained using a test set of transition state optimizations.
- Published
- 2016
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7. Vibrational circular dichroism spectroscopy for probing the expression of chirality in mechanically planar chiral rotaxanes.
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Koenis, Mark A. J., Chibueze, C. S., Jinks, M. A., Nicu, Valentin P., Visscher, Lucas, Goldup, S. M., and Buma, Wybren J.
- Published
- 2020
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8. Systematic Computational Design and Optimization of Light Absorbing Dyes.
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Belić, Jelena, van Beek, Bas, Menzel, Jan Paul, Buda, Francesco, and Visscher, Lucas
- Published
- 2020
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9. Calculating energy derivatives for quantum chemistry on a quantum computer.
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O'Brien, Thomas E., Senjean, Bruno, Sagastizabal, Ramiro, Bonet-Monroig, Xavier, Dutkiewicz, Alicja, Buda, Francesco, DiCarlo, Leonardo, and Visscher, Lucas
- Abstract
Modeling chemical reactions and complicated molecular systems has been proposed as the "killer application" of a future quantum computer. Accurate calculations of derivatives of molecular eigenenergies are essential toward this end, allowing for geometry optimization, transition state searches, predictions of the response to an applied electric or magnetic field, and molecular dynamics simulations. In this work, we survey methods to calculate energy derivatives, and present two new methods: one based on quantum phase estimation, the other on a low-order response approximation. We calculate asymptotic error bounds and approximate computational scalings for the methods presented. Implementing these methods, we perform geometry optimization on an experimental quantum processor, estimating the equilibrium bond length of the dihydrogen molecule to within 0.014 Å of the full configuration interaction value. Within the same experiment, we estimate the polarizability of the H 2 molecule, finding agreement at the equilibrium bond length to within 0.06 a.u. ( 2 % relative error). [ABSTRACT FROM AUTHOR]
- Published
- 2019
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10. Workflows Automation in Computational Chemistry
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zapata, Felipe, Ridder, Lars, Hidding, Johan, Gangarapu, Satesh, Infante, Ivan, and Visscher, Lucas
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automation quantum chemistry python materials - Abstract
Research on modern computational quantum chemistry relies on a set of computational tools to carry out calculations. The complexity of the calculations usually requires intercommunication between the different simulation tools, such communication is usually done through shell scripts that try to automate input/output actions like: write some input for a target quantum chemistry code; submit the calculation to a supercomputer using some sort of queue system like Slurm or Torque; resume in case of a recoverable failure; analyze the output data both manually or with some kind of script; and finally perform several post-processing steps over the raw data. Such scripts are difficult to maintain and extend, requiring both a significant programming expertise to work with them and constant user intervention, resulting in a sub-optimal use of the valuable computational resources. Also as the workflows complexity increase, the manual approach is impractical due to the among of data that must be analysed. Being then desirable a set of automatic and extensible tools that allows to perform complex simulations in heterogeneous hardware platforms. In this work, we present a Python Software to carry out complex simulations in an extensible and automatic way. We also present its application to the simulation of the nonadiabatic molecular dynamics of quantum dots.
- Published
- 2016
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11. Benchmarking electronic structure calculations on the bare [U[O.sub.2].sup.2+] ion: how different are single and multireference electron correlation methods?
- Author
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Real, Florent, Gomes, Andre Severo Pereira, Visscher, Lucas, Vallet, Valerie, and Eliav, Ephraim
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Actinide elements -- Chemical properties ,Excited state chemistry -- Analysis ,Spectrum analysis -- Usage ,Spin coupling -- Analysis ,Chemicals, plastics and rubber industries - Published
- 2009
12. NMR solvent shifts of acetonitrile from frozen density embedding calculations
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Bulo, Rosa E., Jacob, Christoph R., and Visscher, Lucas
- Subjects
Acetonitrile -- Chemical properties ,Acetonitrile -- Mechanical properties ,Acetonitrile -- Spectra ,Nuclear magnetic resonance spectroscopy -- Analysis ,Density functionals -- Analysis ,Chloroform -- Chemical properties ,Chemicals, plastics and rubber industries - Abstract
A density functional theory is used to determine the solvent effect on nuclear magnetic shielding parameters by using example of sensitive nitrogen shift of acetonitrile immersed in a selected set of solvents, like water, chloroform, and cyclohexane. The structural errors introduced can be largely avoided by employing the more expensive and accurate Car-Parrinello molecular dynamics simulations method to generate the ensemble of configurations.
- Published
- 2008
13. Infrared spectroscopy of discrete uranyl anion complexes
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Greoenwold, Gary S., Gianotto, Anita K., McIlwain, Michael E., Stipdonk, Michael J. Van, Kullman, Michael, Moore, David T., Polfer, Nick, Oomens, Jos, Infante, Ivan, Visscher, Lucas, Siboulet, Bertrand, and Jong, Wibe A. de
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Photolysis -- Research ,Infrared spectroscopy -- Usage ,Ionic solutions -- Research ,Dissociation -- Research ,Chemicals, plastics and rubber industries - Abstract
The studies of the wavelength-resolved multiple photon photodissociation of discrete, gas-phase uranyl complexes containing a single anionic ligand with or without ligated solvent molecule is presented. The comparison between the uranyl frequencies and [[U[O.sub.2]AS].sup.+] species with different solvent neutrals showed the values to decrease with increase in neutral nucleophilicity.
- Published
- 2008
14. Taming conformational heterogeneity in and with vibrational circular dichroism spectroscopy.
- Author
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Koenis, Mark A. J., Xia, Yiyin, Domingos, Sérgio R., Visscher, Lucas, Buma, Wybren Jan, and Nicu, Valentin P.
- Published
- 2019
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15. Relativistic general-order coupled-cluster method for high-precision calculations: Application to Al+ atomic clock
- Author
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Kallay, Mihaly, Sahoo, B. K., Nataraj, H. S., Das, B. P., and Visscher, Lucas
- Subjects
Chemical Physics (physics.chem-ph) ,Atomic Physics (physics.atom-ph) ,Physics - Chemical Physics ,FOS: Physical sciences ,Computational Physics (physics.comp-ph) ,Physics - Computational Physics ,Physics - Atomic Physics - Abstract
We report the implementation of a general-order relativistic coupled-cluster method for performing high-precision calculations of atomic and molecular properties. As a first application, the static dipole polarizabilities of the ground and first excited states of Al+ have been determined to precisely estimate the uncertainty associated with the BBR shift of its clock frequency measurement. The obtained relative BBR shift is -3.66+-0.44 for the 3s^2 ^1S_0^0 --> 3s3p ^3P_0^0 transition in Al+ in contrast to the value obtained in the latest clock frequency measurement, -9+-3 [Phys. Rev. Lett. 104, 070802 (2010)]. The method developed in the present work can be employed to study a variety of subtle effects such as fundamental symmetry violations in atoms., 4 pages, 3 tables, submitted
- Published
- 2010
16. Infrared spectroscopy of discrete uranyl anion complexes
- Author
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Groenewold, Gary, Gianotto, Anita, McIlwain, Michael, Van Stipdonk, Michael, Kullman, Michael, Cooper, Travis, Moore, David, Polfer, Nick, Oomens, Jos, Infante, Ivan, Visscher, Lucas, Siboulet, Bertrand, de Jong, Wibe, Idaho National Laboratory, Idaho Falls, ID 83415-2107., Idaho National Laboratory (INL), Wichita State University, FOM Institute for Atomic and Molecular Physics (AMOLF), FOM Institute for Plasma Physics (RIJNHUIZEN), the Netherlands Organization for Scientific Research, Amsterdam Center for Multiscale Modeling, Vrije Universiteit Amsterdam [Amsterdam] (VU), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Pacific Northwest National Laboratory (PNNL), and Theoretical Chemistry
- Subjects
[PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th] ,Analytical chemistry ,Infrared spectroscopy ,Physics::Optics ,coordination complex ,free electron laser ,Methoxide ,[PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex] ,010402 general chemistry ,01 natural sciences ,DFT ,chemistry.chemical_compound ,IRMPD ,Molecule ,Physical and Theoretical Chemistry ,Acetonitrile ,Astrophysics::Galaxy Astrophysics ,mass spectrometry ,010405 organic chemistry ,Chemistry ,Ligand ,actinide ,Photodissociation ,Uranyl ,0104 chemical sciences ,Physical chemistry ,Hydroxide ,SDG 6 - Clean Water and Sanitation - Abstract
International audience; The Free-Electron Laser for Infrared Experiments (FELIX) was used to study the wavelength-resolved multiple photon photodissociation of discrete, gas-phase uranyl (UO$_2$$^{2+}$) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO$_2$A(S)$_n$]$^+$, where A was hydroxide, methoxide, or acetate; S was water, ammonia, acetone, or acetonitrile; and n = 0−3. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO$_2$A]$^+$) were as low or lower than measurements for [UO$_2$]$^{2+}$ ligated with as many as five strong neutral donor ligands and are comparable to solution-phase values. This result was surprising because initial DFT calculations predicted values that were 30−40 cm$^{-1}$ higher, consistent with intuition but not with the data. Modification of the basis sets and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO$_2$A]$^+$ produced [UO$_2$AS]$^+$, which produced only very modest changes to the uranyl antisymmetric stretch frequency, and did not universally shift the frequency to lower values. DFT calculations for [UO$_2$AS]$^+$ were in accord with trends in the data and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO$_2$AS]$^+$ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.
- Published
- 2008
17. Relativity and Electron Correlation in Chemistry
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Visscher, Lucas, Faculty of Science and Engineering, and University of Groningen
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roefschriften (vorm) ,Nuclear Theory ,Dirac-vergelijking, Configuratie-interactie, Elektroncorrela ,kwantumchemie, chemische binding ,Relativistische benadering - Abstract
In this thesis we describe a method for relativistic quantum mechanical calculations on molecules. We obtain relativistic zero order wave functions by the use of the Dirac-Fock method and improve these by relativistic Configuration Interaction. This opens the way for an accurate ab initio treatment of both relativity and electron correlation in molecules or clusters that contain one or more heavy nuclei. ... Zie: Summary
- Published
- 1993
18. Charge-Transfer Excitationsin Uranyl Tetrachloride([UO2Cl4]2â): How Reliableare Electronic Spectra from Relativistic Time-Dependent Density FunctionalTheory?
- Author
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Tecmer, PaweÅ, Bast, Radovan, Ruud, Kenneth, and Visscher, Lucas
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- 2012
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19. High accuracy theoretical investigations of CaF, SrF, and BaF and implications for laser-cooling
- Author
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Hao, Yongliang, Pa��teka, Luka�� F., Visscher, Lucas, collaboration, the NL-eEDM, Aggarwal, Parul, Bethlem, Hendrick L., Boeschoten, Alexander, Borschevsky, Anastasia, Denis, Malika, Esajas, Kevin, Hoekstra, Steven, Jungmann, Klaus, Marshall, Virginia R., Meijknecht, Thomas B., Mooij, Maarten C., Timmermans, Rob G. E., Touwen, Anno, Ubachs, Wim, Willmann, Lorenz, Yin, Yanning, Zapara, Artem, AIMMS, Theoretical Chemistry, LaserLaB - Physics of Light, Atoms, Molecules, Lasers, High-Energy Frontier, Precision Frontier, and Van Swinderen Institute for Particle Physics and G
- Subjects
Atomic Physics (physics.atom-ph) ,FOS: Physical sciences ,ALKALINE-EARTH MONOHALIDES ,General Physics and Astronomy ,MOLECULAR-BEAM ,010402 general chemistry ,01 natural sciences ,Physics - Atomic Physics ,OPTICAL DOUBLE-RESONANCE ,ELECTRIC-DIPOLE MOMENT ,Laser cooling ,0103 physical sciences ,WAVE-FUNCTIONS ,Physics::Atomic Physics ,SDG 7 - Affordable and Clean Energy ,RADIATIVE LIFETIMES ,Physical and Theoretical Chemistry ,Hyperfine structure ,RESOLVED MEASUREMENTS ,Physics ,Quantum Physics ,010304 chemical physics ,LIFETIME MEASUREMENTS ,Multireference configuration interaction ,0104 chemical sciences ,Dipole ,Electric dipole moment ,Coupled cluster ,EXCITED-STATES ,Excited state ,HYPERFINE-STRUCTURE ,Atomic physics ,Quantum Physics (quant-ph) ,Relativistic quantum chemistry ,Physics - Optics ,Optics (physics.optics) - Abstract
The NL-eEDM collaboration is building an experimental setup to search for the permanent electric dipole moment of the electron in a slow beam of cold barium fluoride molecules [Eur. Phys. J. D, 72, 197 (2018)]. Knowledge of molecular properties of BaF is thus needed to plan the measurements and in particular to determine an optimal laser-cooling scheme. Accurate and reliable theoretical predictions of these properties require incorporation of both high-order correlation and relativistic effects in the calculations. In this work theoretical investigations of the ground and the lowest excited states of BaF and its lighter homologues, CaF and SrF, are carried out in the framework of the relativistic Fock-space coupled cluster (FSCC) and multireference configuration interaction (MRCI) methods. Using the calculated molecular properties, we determine the Franck-Condon factors (FCFs) for the $A^2\Pi_{1/2} \rightarrow X^2\Sigma^{+}_{1/2}$ transition, which was successfully used for cooling CaF and SrF and is now considered for BaF. For all three species, the FCFs are found to be highly diagonal. Calculations are also performed for the $B^2\Sigma^{+}_{1/2} \rightarrow X^2\Sigma^{+}_{1/2}$ transition recently exploited for laser-cooling of CaF; it is shown that this transition is not suitable for laser-cooling of BaF, due to the non-diagonal nature of the FCFs in this system. Special attention is given to the properties of the $A'^2\Delta$ state, which in the case of BaF causes a leak channel, in contrast to CaF and SrF species where this state is energetically above the excited states used in laser-cooling. We also present the dipole moments of the ground and the excited states of the three molecules and the transition dipole moments (TDMs) between the different states., Comment: Minor changes; The following article has been submitted to the Journal of Chemical Physics. After it is published, it will be found at https://publishing.aip.org/resources/librarians/products/journals/
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20. A Resolution of Identity Technique to Speed up TDDFT with Hybrid Functionals: Implementation and Application to the Magic Cluster Series Au 8 n +4 (SC 6 H 5 ) 4 n +8 ( n = 3-6).
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D'Antoni P, Medves M, Toffoli D, Fortunelli A, Stener M, and Visscher L
- Abstract
The Resolution of Identity (RI) technique has been employed to speed up the use of hybrid exchange-correlation (xc) functionals at the TDDFT level using the Hybrid Diagonal Approximation. The RI has been implemented within the polTDDFT algorithm (a complex damped polarization method) in the AMS/ADF suite of programs. A speedup factor of 30 has been obtained with respect to a previous numerical implementation, albeit with the same level of accuracy. Comparison of TDDFT simulations with the experimental photoabsorption spectra of the cluster series Au
8 n +4 (SR)4 n +8 ( n = 3-6; R = C6 H5 ) showed the excellent accuracy and efficiency of the method. Results were compared with those obtained via the more simplified and computationally cheaper TDDFT+TB and sTDDFT methods. The present method represents an accurate as well as computationally affordable approach to predict photoabsorption spectra of complex species, realizing an optimal compromise between accuracy and computational efficiency, and is suitable for applications to large metal clusters with sizes up to several hundreds of atoms.- Published
- 2023
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21. Low-Order Scaling Quasiparticle Self-Consistent GW for Molecules.
- Author
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Förster A and Visscher L
- Abstract
Low-order scaling GW implementations for molecules are usually restricted to approximations with diagonal self-energy. Here, we present an all-electron implementation of quasiparticle self-consistent GW for molecular systems. We use an efficient algorithm for the evaluation of the self-energy in imaginary time, from which a static non-local exchange-correlation potential is calculated via analytical continuation. By using a direct inversion of iterative subspace method, fast and stable convergence is achieved for almost all molecules in the GW100 database. Exceptions are systems which are associated with a breakdown of the single quasiparticle picture in the valence region. The implementation is proven to be starting point independent and good agreement of QP energies with other codes is observed. We demonstrate the computational efficiency of the new implementation by calculating the quasiparticle spectrum of a DNA oligomer with 1,220 electrons using a basis of 6,300 atomic orbitals in less than 4 days on a single compute node with 16 cores. We use then our implementation to study the dependence of quasiparticle energies of DNA oligomers consisting of adenine-thymine pairs on the oligomer size. The first ionization potential in vacuum decreases by nearly 1 electron volt and the electron affinity increases by 0.4 eV going from the smallest to the largest considered oligomer. This shows that the DNA environment stabilizes the hole/electron resulting from photoexcitation/photoattachment. Upon inclusion of the aqueous environment via a polarizable continuum model, the differences between the ionization potentials reduce to 130 meV, demonstrating that the solvent effectively compensates for the stabilizing effect of the DNA environment. The electron affinities of the different oligomers are almost identical in the aqueous environment., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Förster and Visscher.)
- Published
- 2021
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22. Understanding the Relation between Structural and Spectral Properties of Light-Harvesting Complex II.
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Sen S, Mascoli V, Liguori N, Croce R, and Visscher L
- Subjects
- Chlorophyll chemistry, Chlorophyll radiation effects, Density Functional Theory, Light, Light-Harvesting Protein Complexes radiation effects, Models, Chemical, Spectrophotometry, Light-Harvesting Protein Complexes chemistry
- Abstract
Light-harvesting complex II (LHCII) is a pigment-protein complex present in higher plants and green algae. LHCII represents the main site of light absorption, and its role is to transfer the excitation energy toward the photosynthetic reaction centers, where primary energy conversion reactions take place. The optical properties of LHCII are known to depend on protein conformation. However, the relation between the structural and spectroscopic properties of the pigments is not fully understood yet. In this respect, previous classical molecular dynamics simulations of LHCII in a model membrane [ Sci. Rep. 2015 , 5 , 1-10] have shown that the configuration and excitonic coupling of a chlorophyll (Chl) dimer functioning as the main terminal emitter of the complex are particularly sensitive to conformational changes. Here, we use quantum chemistry calculations to investigate in greater detail the effect of pigment-pigment interactions on the excited-state landscape. While most previous studies have used a local picture in which electrons are localized on single pigments, here we achieve a more accurate description of the Chl dimer by adopting a supramolecular picture where time-dependent density functional theory is applied to the whole system at once. Our results show that specific dimer configurations characterized by shorter inter-pigment distances can result in a sizable intensity decrease (up to 36%) of the Chl absorption bands in the visible spectral region. Such a decrease can be predicted only when accounting for Chl-Chl charge-transfer excitations, which is possible using the above-mentioned supramolecular approach. The charge-transfer character of the excitations is quantified by two types of analyses: one focusing on the composition of the excitations and the other directly on the observable total absorption intensities.
- Published
- 2021
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23. Not Completely Innocent: How Argon Binding Perturbs Cationic Copper Clusters.
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Jamshidi Z, Lushchikova OV, Bakker JM, and Visscher L
- Abstract
Argon is often considered as an innocent probe that can be attached and detached to study the structure of a particular species without perturbing the species too much. We have investigated whether this assumption also holds for small copper cationic clusters and demonstrated that small but significant charge transfer from argon to metal changes the remaining binding positions, leading in general, to weaker binding of other argon atoms. The exception is binding to just one copper ion, where the binding of the first argon facilitates the binding of the second.
- Published
- 2020
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24. Analysis of Vibrational Circular Dichroism Spectra of Peptides: A Generalized Coupled Oscillator Approach of a Small Peptide Model Using VCDtools.
- Author
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Koenis MAJ, Visscher L, Buma WJ, and Nicu VP
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- Hydrogen Bonding, Models, Molecular, Protein Conformation, alpha-Helical, Protein Conformation, beta-Strand, Circular Dichroism, Peptides chemistry
- Abstract
Vibrational circular dichroism (VCD) is one of the major spectroscopic tools to study peptides. Nevertheless, a full understanding of what determines the signs and intensities of VCD bands of these compounds in the amide I and amide II spectral regions is still far from complete. In the present work, we study the origin of these VCD signals using the general coupled oscillator (GCO) analysis, a novel approach that has recently been developed. We apply this approach to the ForValNHMe model peptide in both α-helix and β-sheet configurations. We show that the intense VCD signals observed in the amide I and amide II spectral regions essentially have the same underlying mechanism, namely, the through-space coupling of electric dipoles. The crucial role played by intramolecular hydrogen bonds in determining VCD intensities is also illustrated. Moreover, we find that the contributions to the rotational strengths, considered to be insignificant in standard VCD models, may have sizable magnitudes and can thus not always be neglected. In addition, the VCD robustness of the amide I and II modes has been investigated by monitoring the variation of the rotational strength and its contributing terms during linear transit scans and by performing calculations with different computational parameters. From these studies-and in particular, the decomposition of the rotational strength made possible by the GCO analysis-it becomes clear that one should be cautious when employing measures of robustness as proposed previously.
- Published
- 2020
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25. Water Adsorption on Free Cobalt Cluster Cations.
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Kiawi DM, Bakker JM, Oomens J, Buma WJ, Jamshidi Z, Visscher L, and Waters LB
- Abstract
Cationic cobalt clusters complexed with water Con(+)-H2O (n = 6-20) are produced through laser ablation and investigated via infrared multiple photon dissociation (IR-MPD) spectroscopy in the 200-1700 cm(-1) spectral range. All spectra exhibit a resonance close to the 1595 cm(-1) frequency of the free water bending vibration, indicating that the water molecule remains intact upon adsorption. For n = 6, the frequency of this band is blue-shifted, but it gradually converges to the free water value with increasing cluster size. In the lower-frequency range (200-650 cm(-1)) the spectra contain several bands which show a very regular frequency evolution, suggesting that the exact cluster geometry has little effect on the water-surface interaction. Density functional theory (DFT) calculations are carried out at the OPBE/TZP level for three representative sizes (n = 6, 9, 13) and indicate that the vibrations responsible for the resonances correspond to bending and torsional modes between the cluster and water moieties. The potential energy surfaces describing these interactions are very shallow, making the calculated harmonic frequencies and IR intensities very sensitive to small geometrical perturbations. We conclude that harmonic frequency calculations on (local) minima structures provide insufficient information for these types of cluster complexes and need to be complemented with calculations that provide a more extensive sampling of the potential energy surface.
- Published
- 2015
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26. Charge-transfer excitations in uranyl tetrachloride ([UO2Cl4]2-): how reliable are electronic spectra from relativistic time-dependent density functional theory?
- Author
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Tecmer P, Bast R, Ruud K, and Visscher L
- Subjects
- Energy Transfer, Models, Molecular, Quantum Theory, Static Electricity, Thermodynamics, Time Factors, Vibration, Chlorides chemistry, Uranium Compounds chemistry
- Abstract
Four-component relativistic time-dependent density functional theory (TD-DFT) is used to study charge-transfer (CT) excitation energies of the uranyl molecule as well as the uranyl tetrachloride complex. Adiabatic excitation energies and vibrational frequencies of the excited states are calculated for the lower energy range of the spectrum. The results for TD-DFT with the CAM-B3LYP exchange-correlation functional for the [UO(2)Cl(4)](2-) system are in good agreement with the experimentally observed spectrum of this species and agree also rather well with other theoretical data. Use of the global hybrid B3LYP gives qualitatively correct results, while use of the BLYP functional yields results that are qualitatively wrong due to the too low CT states calculated with this functional. The applicability of the overlap diagnostic of Peach et al. (J. Chem. Phys.2008, 128, 044118) to identify such CT excitations is investigated for a wide range of vertical transitions using results obtained with three different approximate exchange-correlation functionals: BLYP, B3LYP, and CAM-B3LYP.
- Published
- 2012
- Full Text
- View/download PDF
27. Computational study on the anomalous fluorescence behavior of isoflavones.
- Author
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Beyhan SM, Götz AW, Ariese F, Visscher L, and Gooijer C
- Subjects
- Absorption, Computer Simulation, Models, Molecular, Molecular Conformation, Solvents chemistry, Spectrometry, Fluorescence, Water chemistry, Fluorescence, Isoflavones chemistry, Quantum Theory
- Abstract
Isoflavones are known to show fluorescence with intensities that depend strongly on the solvent properties and exhibit Stokes' shifts as large as 1.4 eV. While some of this behavior can be explained by (excited state) deprotonation, this mechanism does not apply for all isoflavones. The aim of this study is to computationally and experimentally investigate the reasons for this anomalous behavior of neutral isoflavones, taking the daidzein molecule as a model compound. We find that the absence in fluorescence in aprotic solvents and the weak fluorescence in protic solvents can be explained by a change of order of the lowest singlet states in which a fluorescent charge-transfer state lies below the nonfluorescent locally excited state in water but not in acetonitrile. The large Stokes' shift is partly due to a significant rotation among the chromone-phenyl bond in the excited state.
- Published
- 2011
- Full Text
- View/download PDF
28. Infrared spectroscopy of discrete uranyl anion complexes.
- Author
-
Groenewold GS, Gianotto AK, McIlwain ME, Stipdonk MJ, Kullman M, Moore DT, Polfer N, Oomens J, Infante I, Visscher L, Siboulet B, and Jong WA
- Abstract
The Free-Electron Laser for Infrared Experiments (FELIX) was used to study the wavelength-resolved multiple photon photodissociation of discrete, gas-phase uranyl (UO22+) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO2A(S)n]+, where A was hydroxide, methoxide, or acetate; S was water, ammonia, acetone, or acetonitrile; and n = 0-3. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO2A]+) were as low or lower than measurements for [UO2]2+ ligated with as many as five strong neutral donor ligands and are comparable to solution-phase values. This result was surprising because initial DFT calculations predicted values that were 30-40 cm(-1) higher, consistent with intuition but not with the data. Modification of the basis sets and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO2A]+ produced [UO2AS]+, which produced only very modest changes to the uranyl antisymmetric stretch frequency, and did not universally shift the frequency to lower values. DFT calculations for [UO2AS]+ were in accord with trends in the data and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO2AS]+ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.
- Published
- 2008
- Full Text
- View/download PDF
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