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The bimolecular recombination characteristics of conjugated polymer poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,5-bis 3-tetradecylthiophen-2-yl thiazolo 5,4-d thiazole)-2,5diyl] (PDTSiTTz) blended with the fullerene series PC60BM, ICMA, ICBA, and ICTA have been investigated using microsecond and femtosecond transient absorption spectroscopy, in conjunction with electroluminescence measurements and ambient photoemission spectroscopy. The non-Langevin polymer PDTSiTTz allows an inspection of intrinsic bimolecular recombination rates uninhibited by diffusion, while the low oscillator strengths of fullerenes allow polymer features to dominate, and we compare our results to those of the well-known polymer Si-PCPDTBT. Using μs-TAS, we have shown that the trap-limited decay dynamics of the PDTSiTTz polaron becomes progressively slower across the fullerene series, while those of Si-PCPDTBT are invariant. Electroluminescence measurements showed an unusual double peak in pristine PDTSiTTz, attributed to a low energy intragap charge transfer state, likely interchain in nature. Furthermore, while the pristine PDTSiTTz showed a broad, low-intensity density of states, the ICBA and ICTA blends presented a virtually identical DOS to Si-PCPDTBT and its blends. This has been attributed to a shift from a delocalized, interchain highest occupied molecular orbital (HOMO) in the pristine material to a dithienosilole-centered HOMO in the blends, likely a result of the bulky fullerenes increasing interchain separation. This HOMO localization had a side effect of progressively shifting the polymer HOMO to shallower energies, which was correlated with the observed decrease in bimolecular recombination rate and increased “trap” depth. However, since the density of tail states remained the same, this suggests that the traditional viewpoint of “trapping” being dominated by tail states may not encompass the full picture and that the breadth of the DOS may also have a strong influence on bimolecular recombination.

Lithium cobalt pyrophosphate (LCPO) is a promising cathode material for solid-state batteries due to its intrinsic high-voltage characteristic. Using density functional theory calculations, we reve...

We present the first atomistic-scale simulation of the discharge process of polymeric cathode materials for electrochemical batteries in solid state. The oxidation of polyaniline (PANI) and of cyano groups (CN) functionalized PANI induced by coordination to the electrolyte anions is computed and voltage curves are estimated. To deal with the large required numbers of atoms and structures, a combination of molecular dynamics and density functional tight binding (DFTB) is used. The DFTB is benchmarked to density functional theory (DFT) calculations using different functionals to confirm its accuracy. The voltages computed with the solid state model are in good agreement with available experimental data and ab initio models based on oligomers. The solid state model also predicts substantially increased voltage with PANI functionalized with cyano groups.

High temperature oxidation of 300 nm single crystalline Ti2AlN MAX phase thin film deposited on MgO(111) substrate between 300 and 900 °C has been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and mass spectrometry. As shown by XRD, Ti2AlN remained structurally stable up to 700 °C, before it began to react with MgO substrate and ambient O2 to form MgTi2O5 and MgAl2O4 at 900 °C. However, as revealed by XPS, oxidation of Ti2AlN occurred at room temperature from its surface by forming TiO2, TiNxOy and Al2O3 with surface enrichment of Al. This initial oxidation continued up to 300 °C, until Ti and Al in the surface layer (∼7.1 nm thick) have been completely oxidized into TiO2 and Al2O3 at 500 °C, where Al in the subsurface preferentially diffused to the edges of the terraces and agglomerated into Al2O3 islands. At 700 °C and above, surface of Ti2AlN lost its characteristic hexagonal terrace morphology by transforming into round islands as a res...

The reaction mechanism for the in situ prepared Pd-Cy*Phine catalyst used in copper-free Sonogashira coupling was investigated using density functional theory. In addition, the significance of the meta-terarylphosphine ligand architecture of Cy*Phine was probed, as it had been previously shown experimentally to augment catalytic activity relative to its biarylphosphine analogue, XPhos. The calculated reaction barriers and free energies for the steps in the catalytic cycle suggest that the suppression of a dearomative rearrangement pathway is likely to be an important feature for the improved catalytic performance observed for the Pd-Cy*Phine system.

Halogen bonding (XB) has become one of the most studied non-covalent interactions in the past two decades, owing to its wide range of applications in materials and biological applications. Most of the current theoretical and experimental studies focus on XB involving lone-pair acceptors due to its predictability in terms of crystal geometries. However, recent reports have advocated the importance of XB materials involving aromatic-type acceptors because of their relevance in functional materials, catalysis and biological systems. Herein, we report the XB site-specificity in several polycyclic aromatic hydrocarbons (PAHs) and N-heteroaromatic compounds that are ubiquitous in chemical systems. Based on a series of quantum chemical studies of Cl2 and Br2 XB complexes with 14 representative systems, these XB sites can be easily predicted using occupied molecular orbitals and atomic charges. We envisage that the predicted site maps will be useful for materials and drug design involving this class of non-covalent interactions.

Computations (density functional theory) of the post-transmetallation stages (carborhodation, 1,4-shift consisting of C–H oxidative addition/C–H reductive elimination, and hydrolysis) in the catalytic cycle for the arylation of 2-butyne with phenylboronic acid mediated by [(dppe)RhI] catalyst [dppe = 1,2-bis(diphenylphosphanyl)ethane] shows that (1) carborhodation is facile (ΔG‡ ≈ 10 kcal mol–1); (2) the barriers of the 1,4-shift and hydrolysis are approximately equal (ΔG‡ ≈ 19–24 kcal mol–1); (3) the 1,4-Rh shift product is ca. 5 kcal mol–1 more stable than the non-rearranged product, in good agreement with the experimental results. Analogous computations for (Z)-2-butene as a model substrate show that (1) carborhodation is much slower (ΔG‡ ≈ 19 kcal mol–1); (2) the sp3 → sp2 1,4-shift is faster than the sp2 → sp2 1,4-shift; (3) the hydrolysis of Rh–C σ bonds depends more on the steric environment than the hybridization of the C atom; and (4) β-hydride elimination is the most likely reaction after carborhodation.

To understand the origin of the Al deficient Ti2AlN MAX phase observed in our experiments, the formation and the diffusion pathway of Al vacancy in Ti2AlN have been calculated by density functional theory (DFT). Compared to Ti and N vacancies, Al vacancies require the lowest formation energies not only in the bulk but also at the top surface layer and the second surface layer. As a result, Ti2AlN is calculated to be capable of accommodating Al vacancies in the supercell down to a substoichiometric Ti2Al0.75N while maintaining the MAX phase structure. After the vacancy formation, Al atom is calculated to diffuse along the (0001) plane preferentially via vacancy jump with an energy barrier of 0.80 eV, leading to Al surface segregation and subsequent desorption from Ti2AlN at high temperatures.

We report first principles calculations aimed at understanding the dopant chemical potential modulation on the oxygen vacancy formation in In 2 O 3 . Relaying on our results, it implies that oxygen vacancies are deep donors in undoped In 2 O 3 and change to shallow donors with embedded Zn and Al in contrast to previous expectations of native carrier from oxygen vacancy. Our results well explain the anomalous carrier concentration increase in Zn and Al codoped In 2 O 3 . Our proposed models reveal the chemical potential modulation on oxygen vacancy formation and lead to a natural oxygen vacancy formation mechanism in the presence of metallic dopants in In 2 O 3 .

The exposed surface facets play an important role in determining the catalytic performance of nanostructured materials. In this study, we report the synthesis of hematite nanoparticles with three varying morphologies with exposure of well-controlled {104}, {113} and {001} surfaces. The better shape control of hematite particles has provided a direct correlation between the surface facets and the photocatalytic performance. The catalytic photodegradation of MB using hematite nanoparticles reveals that the reaction follows the heterogeneous photo-Fenton process under visible light irradiation. The catalytic performance of hematite surface facets follows the order of {113} > {104} > {001}. Density functional theory (DFT) calculations were conducted to demonstrate the atomic surface structures and the corresponding charge distribution. The results indicate that the catalytic activity depends on surface atom arrangements as well as the number and the type of surface terminated hydroxyl groups bonding to underlying Fe atoms, where low valence states of Fe on {104} and {113} planes have the highest probability to be oxidized by H2O2 and the concurrently generated Fe(3+x)+ sites are more electronegative to accept electrons from activated dye molecules. The findings are of fundamental importance to understand the surface-dependence of photocatalytic properties, thus shedding new light on the catalytic application of hematite particles.

Computational studies using correlated wave function methods and density functional theory were carried out on a series of acetylene-linked bimane oligomers with particular emphasis on their excitonic properties and implications for intra-chain excitation energy transfer (EET). The low energy barriers found for the rotation of bimane subunits about the longitudinal axis are such that the π-conjugation is easily disrupted. Nevertheless, a distinctive feature of the oligomer lies in the parallel alignment of the S1 transition dipole along the longitudinal axis, which sustains electronic coupling between adjacent bimane subunits over a range of torsional angles and is crucial for driving intra-chain EET. Using a model that comprises hexameric donor and acceptor fragments, we evaluated electronic couplings and spectral overlaps, and applied Fermi's golden rule (in the weak electronic coupling regime) to approximate the lower limit of intra-chain EET in an acetylene-linked bimane photonic wire.

Fluorescence lifetimes were evaluated using TD-DFT under different approximations for the emitting molecule and various exchange–correlation functionals, such as B3LYP, BMK, CAM-B3LYP, LC-BLYP, M06, M06-2X, M11, PBE0, ωB97, ωB97X, LC-BLYP*, and ωB97X* where the range-separation parameters in the last two functionals were tuned in a non-empirical fashion. Changes in the optimised molecular geometries between the ground and electronically excited states were found to affect the quality of the calculated lifetimes significantly, while the inclusion of vibronic features led to further improvements over the assumption of a vertical electronic transition. The LC-BLYP* functional was found to return the most accurate fluorescence lifetimes with unsigned errors that are mostly within 1.5 ns of experimental values.

Phase stability of single-crystalline Ti2AlN thin film in ultra-high vacuum has been studied in situ by X-ray photoelectron spectroscopy as a function of annealing temperature and ex situ by atomic force microscopy, secondary ion mass spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and nanoindentation. Ti2AlN is stable up to 600 °C. At 700 °C, Al is preferentially desorbed from the surface and becomes nearly undetected at 900 °C by XPS, where single-crystalline Ti2AlN with terrace morphology transforms into polycrystalline δ-TiN1–x and ξ-TiN0.75–y phases with voids on the surface and reduced film thickness. Mechanical properties including hardness and Young’s modulus are also observed to have deteriorated. Density functional theory calculation shows that Al atoms prefer to diffuse out from the Ti2AlN horizontally along the Al basal planes. The subsequent desorption of Al from surface due to its high vapor pressure results in the decreased Al composition, the void formation on the su...

Single-crystalline Ti2AlN thin films have been grown on MgO(111) substrates at 750 °C using DC magnetron sputtering from a Ti2Al alloy target in a mixed N2/Ar plasma. X-ray diffraction and transmission electron microscopy confirm epitaxial layered growth of Ti2AlN (0001) on MgO(111). On the basis of the experimental results, ab initio calculations were carried out to study the geometry and electronic structure between Ti2AlN and oxygen/magnesium -terminated MgO polar surfaces. A total of eight interface structures were calculated, and results showed that the adhesion between Ti2AlN (0001) and O-terminated MgO(111) is stronger than that with Mg-terminated MgO(111) surfaces in general. In particular, the largest adhesion energy was found for the interfacial structure with N–Ti–Al–Ti/O–Mg configuration. The stronger adhesion is due to reactive nature of Ti2AlN surface with N–Ti–Al–Ti stacking sequence. In addition, electronic structure calculation results showed that there is charge transferring between Ti2A...

A series of four novel n-type molecules has been synthesized. Unlike previous approaches, the end group of these molecules was fixed and the molecular core was varied. The resulting materials were thoroughly analyzed. Electronic properties were derived from photoemission spectroscopy, optical properties were derived with the help of optical spectroscopy, and the structure of thin films on Au(111) was derived by scanning tunneling microscopy (STM). In addition, prototypical organic field-effect transistors (OFETs) (forming n-channels in OFETs) have been fabricated and tested. The correlation between the device performance of the respective OFETs (i.e., electron mobility) and their electronic as well as structural properties was investigated. It turned out that a combination of beneficial electronic and structural properties provides the best results. These findings are important for the design of new materials for future device applications.

Single crystalline Ti2AlN thin films have been grown on MgO(111) substrates at 750 °C using DC magnetron sputtering from a Ti2Al alloy target in a mixed N2/Ar plasma. X-ray diffraction, atomic force microscopy, and transmission electron microscopy demonstrate layered growth of a Ti2AlN{0002} thin film on the MgO(111) substrate. X-ray photoelectron spectroscopy detects a TiN-like conducting nature of the Ti2AlN thin film. However, the binding energies (BEs) of Ti 2p3/2 and Al 2p have shifted to 454.7 ± 0.2 and 72.3 ± 0.2 eV, respectively, lower than their corresponding values in nitrides (TiN and AlN). The BE of Al 2p is even lower than that in metallic Al. The unusual shifts are attributed to charge transfer from Ti to Al as shown by the density functional theory calculations.

Rhodium, nickel, and palladium functionalized single-walled boron nitride nanotubes (SWBNNTs) and their applications to hydrogen storage have been investigated using density functional theory (DFT). Single Rh, Ni, and Pd atoms prefer to bind strongly at the axial bridge site of BN nanotube, and each Rh, Ni and Pd atom bound on BNNT may adsorb up to four, three, and two H2 molecules, respectively, with the H−H bonds of H2 molecules significantly elongated. More H2 molecules would bind with metal atoms and tubes when four metal atoms are dispersed at the bridge sites per cell, the presence of Rh, Ni, and Pd metal atoms leads to high hydrogen storage capacity on BNNTs. In addition, our calculation results also show that the nature of interaction between hydrogen and metal-doped BNNT is due to the hybridization of the metal d orbital with the hydrogen s orbital. Our work not only predicts hydrogen capacities and their binding energies for metal-doped BNNTs but also advances the understanding of the nature of ...

Positive and negative third-order optical nonlinearities have been investigated in single-stranded DNA wrapped semiconducting single-walled carbon nanotubes. It is found that the redox reactions of hydrogen peroxide can reverse the sign of the third-order nonlinearity. The observation proves that the lowest unoccupied molecular orbital has a lower density of electronic states than that of the highest occupied molecular orbital. A three-energy-level model is used to explain the effect of the redox reactions. Raman spectroscopy has also been used to investigate the interaction between single-walled carbon nanotubes and single-stranded DNA.

We performed density functional theory (DFT) calculations to investigate the adsorption of atomic hydrogen (H) on the wrapping axis of nonpolar arm-chair (5,5) and chiral (8,4) boron nitride nanotubes (BNNTs) with a view toward understanding the chemisorption-induced polarization field in BNNTs. The adsorption of H along the zigzag B−N bonds that lie on the wrapping axis of the BNNT enhances the macroscopic polarization field. Depending on whether the B or N site near the edge of the nanotube is adsorbed with H, the direction of the polarization field, as well as the work function of the tube ends, can be changed significantly. The relationship between the chemical effect as well as the geometric distortion of the tube caused by chemisorption and the induced polarization were investigated, respectively. The results have implications for the application of BNNTs as electron emitters.

High-level ab initio calculations, including variants of the Wn and G3 procedures, have been used to determine the structures and heats of formation of the alkali metal and alkaline earth metal oxides and hydroxides (M2O, MOH: M = Li, Na, and K; MO, M(OH)2: M = Be, Mg, and Ca). Our best structures were obtained at the CCSD(T)(riv,rv)/aug‘-cc-pWCVQZ level and are in uniformly close agreement with available experimental data, with a mean absolute deviation from experimental metal−oxygen bond lengths of just 0.007 A.Structures obtained with CCSD(T)/cc-pWCVQZ, B3-LYP/cc-pVTZ, B3-LYP/6-31G(2df,p), and MP2(full)/6-311+G(3df,2p) are also in good agreement with experiment. Zero-point vibrational energies and enthalpy temperature corrections are found to be relatively insensitive to the various procedures employed. However, the heats of formation for these molecules are challenging targets for high-level ab initio procedures. In the Wn-type procedures, it is found that expanding the correlation space on the meta...

The authors gratefully acknowledge generous allocations of computing time on the Compaq Alphaserver of the National Facility of the Australian Partnership for Advanced Computing, Australian National University Supercomputer Facility, and the support of the Australian Research Council.

The electronic structures of the triplet ground states and first three excited singlet states for phenylnitrene, 14 meta-, and 17 para-substituted congeners have been characterized using density functional theory and multireference second-order perturbation theory (CASPT2). Ring expansion pathways to form didehydroazepines have activation enthalpies of about 9 kcal⋅mol−1 and are fairly insensitive to substitution—in the case of the strongest para donor, MeNH–, this barrier increases to about 13 kcal⋅mol−1. The trends in state energies as a function of substitution are rationalized using a (2,2) configuration interaction theory and qualitative molecular orbital theory. Analysis of spin-orbit coupling in the nitrenes using the same model in conjunction with explicit calculation of spin-orbit coupling matrix elements rationalizes why electron donating substituents increase rates of intersystem crossing. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

The red Pechmann dye (λ(max) = 550 nm) is the exo-dimer of 4-phenyl-3-butenolide connected at the α-carbon by a double bond in a trans-fashion. The ring system is easily rearranged to the trans-endo-fused bicyclic 6-membered lactone dimer (yellow). Both lactones can be singly or doubly amidated with primary amines leading to further colour changes. The nature of the core heterocycle (exo- vs. endo-; 5- or 6-membered ring), core heteroatom (O vs. N) and additional substituents on the phenyl ring allows for exquisite control over colour achievable within a single dye family. Herein we present a detailed investigation of the modelling of the electronic spectra of the Pechmann dye family by time-dependent density functional theory (TDDFT). Whereas pure Hartree-Fock (TDHF) ab-initio calculation underestimates the UV/Vis absorption maximum, pure TDDFT leads to a large overestimation. The accuracy of the prediction is highly dependent on the mix of HF and DFT, with BMK (42% HF) and M06-2X (54% HF) giving the closest match with the experimental value. Among all basis sets evaluated, the computationally-efficient, DFT-optimized DGDZVP showed the best chemical accuracy/size profile. Finally, the dispersion interaction-corrected (SMD) implicit solvation model was found to be advantageous compared to the original IEFPCM. The absorption maxima of substituted Pechmann dyes and their rearranged lactone counterparts can be predicted with excellent accuracy (±6 nm) at the optimal SMD(toluene)/TD-BMK/DGDZVP//SMD(toluene)B3LYP/DGDZVP level of theory. Using this procedure, a small virtual library of novel, heterocycle-substituted Pechmann dyes were screened. Such substitution was shown to be a viable strategy for colour tuning, giving λ(max) from 522 (4-pyridyl) to 627 (2-indolyl) nm.

Reactions of three alkynes, namely, 1-heptyne, 3-hexyne and 1-phenyl-1-butyne, with [Rh(4)(CO)(9)(μ-CO)(3)] are performed in anhydrous hexane under argon atmosphere with multiple perturbations of alkynes and [Rh(4)(CO)(9)(μ-CO)(3)]. The reactions are monitored by in situ UV/Vis spectroscopy, and the collected electronic spectra are further analyzed with the band-target entropy minimization (BTEM) family of algorithms to reconstruct the pure component spectra. Three BTEM estimates of [(μ(4)-η(2)-alkyne)Rh(4)(CO)(8)(μ-CO)(2)], in addition to that of [Rh(4)(CO)(9)(μ-CO)(3)], are successfully reconstructed from the experimental spectra. Time-dependent density functional theory (TD-DFT) predicted spectra at the PBE0/DGDZVP level are consistent with the corresponding BTEM estimates. The present study demonstrates that: 1) the BTEM family of algorithms is successful in analyzing multi-component UV/Vis spectra and results in good spectral estimates of the trace organometallics present; and 2) the subsequent DFT/TD-DFT methods provide an interpretation of the nature of the electronic excitation and can be used to predict the electronic spectra of similar transition organometallic complexes.

N,N′-Disubstituted naphthalenediimides (NDIs), planar, electron-deficient building blocks, play an important role in materials and biological sciences. Naphthalene core substituents control the HOMO and LUMO energies, whereas the N-alkyl or aryl substituents affect the solubility, aggregation, and packing propensity in condensed phases. N,N′-Dihydroxynaphthalenediimide (DHNDI) allows expanding the chemical diversity by O-alkylation, acylation, or sulfonylation; these derivatives also allow fine-tuning of the HOMO/LUMO levels. The synthesis, UV–vis, electrochemical, solid state, and computational prediction of the properties of such derivatives are presented.

Using density functional theory calculations, we demonstrate that one-dimensional bimetallic molecular ferromagnets (FeCpMCp)(infinity) (M = Sc, Ti, V, Cr and Mn, Cp = cyclopentadienyl) exhibit significant enhancement in local and global atomic magnetic moments as well as relatively large spin-polarization energy as compared to their monometallic counterparts. These yield an unusual charge configuration for one of the wires: (Fe(0)Cp(-1)V(+2)Cp(-1))(infinity). Hückel's rule and double-exchange interaction model are used to illustrate the details of local charge transfer and long-range ferromagnetic order. We then propose a growth mechanism for V(n)(FeCp(2))(n+1) (n = 1-4) clusters, which is supported unambiguously with time-of-flight mass spectroscopy data.

The geometries, enthalpies of formation (DeltaH(o)(f)), separations of electronic states, electron affinities, gas-phase acidities, and bond dissociation energies associated with the alkali metal monoxide anions (MO(-)), monoxide radicals (MO(*)), and hydroxides (MOH) (M = Li, Na, and K) have been investigated using single-reference and multireference variants of the WnC procedures. Our best estimates of the DeltaH(o)(f) values for the ground states at 298 K are as follows: 8.5 ((3)Pi LiO(-)), 48.5 ((2)Pi LiO(*)), -243.4 ((1)Sigma(+) LiOH), 34.2 ((3)Pi NaO(-)), 86.4 ((2)Pi NaO(*)), -190.8 ((1)Sigma(+) NaOH), 15.1 ((1)Sigma(+) KO(-)), 55.9 ((2)Sigma(+) KO(*)), and -227.0 ((1)Sigma(+) KOH) kJ mol(-1). While the LiO(*) and NaO(*) radicals have (2)Pi ground states, for KO(*), the (2)Sigma(+) and (2)Pi electronic states lie very close in energy, with our best estimate being a preference for the (2)Sigma(+) state by 1.1 kJ mol(-1) at 0 K. In a similar manner, the ground state for MO(-) changes from (3)Pi for LiO(-) and NaO(-) to (1)Sigma(+) for KO(-). The (1)Sigma(+) state of KO(-) is indicated by the calculated T(1) diagnostic and the SCF contribution to the total atomization energy to have a significant degree of multireference character. This leads to a difference of more than 100 kJ mol(-1) between the single-reference W2C and multireference W2C-CAS-ACPF and W2C-CAS-AQCC estimates for the (1)Sigma(+) DeltaH(o)(f) for KO(-).

First-principles calculations were carried out to examine the catalytic activity of Pd and Pd-Au alloy surfaces for CO oxidation. The influences of surface-ligand effect and lattice strain effect on activity were demonstrated. The catalytic efficiency of Pd-Au bimetallic systems depends largely on the surface composition of Pd and Au. The addition of Au significantly improves the activity of a Pd-Au bimetallic slab with an Au-rich surface due to the dominant Au-induced ligand effect on both O and CO chemisorption. Among the various cases considered, the system with Au on the surface of the Pd(16)Au(4) slab exhibits the lowest energy barrier of 0.21 eV, which is decreased by 0.66 eV compared to that of the pure Pd(111) surface. It is predicted that the [Pd](Au) core/shell nanoparticle catalyst should have a higher activity for CO oxidation as it combines the advantages of the ligand effect of Au and the strain effect of Pd.

Cycloaddition of allyl organics on the dimer rows of a clean C(100)-2x1 diamond surface can be used for the controlled functionalization of such a surface. Sticking probability measurements confirm that appreciable uptake of acetylene and butadiene occur on the clean diamond surface at room temperature. The change in electron affinity of the surface as a function of the coverage of the organic molecules is investigated with periodic DFT calculations. The presence of C-H dipoles on these adsorbates modify the surface charge density and gives rise to an induced dipolar layer that modifies the electrostatic potential outside the surface. There is a significant reduction of up to 2.5 eV in electron affinity following the chemisorption of ethylene. Therefore, the adsorbed molecules play the same role as surface hydrogen in inducing the NEA condition on the clean diamond. The change in electron affinity does not scale linearly with the coverage of the organic molecules, because the spatial profile of the C-H dipoles as well as the orientation of the molecules on the surface have a predominant effect on the surface charge density.

A variety of theoretical procedures, including the high-level ab initio methods G3, G3[CC](dir,full), and W2C//ACQ, have been used to predict the structures and heats of formation of several small calcium-containing molecules (CaH, CaH2, CaO, CaOH, Ca(OH)2, CaF, CaF2, CaS, CaCl, and CaCl2). B3-LYP and CCSD(T) with both the (aug-)cc-pWCVQZ and (aug-)cc-pWCVQ+dZ basis sets are found to give molecular geometries that agree well with the experimental results. The CCSD(T)(riv)/(aug-)cc-pWCVQ+dZ results are found to be the most accurate, with a mean absolute deviation from experiment of just 0.008 angstroms. Zero-point vibrational energies (ZPVEs) and thermochemical corrections are found to be relatively insensitive to the level of theory, except in the case of molecules with highly anharmonic calcium-centered bending modes (CaH2, Ca(OH)2, CaF2, CaCl2), where special procedures need to be employed in order to obtain satisfactory results. Several potential improvements to the W2C method were investigated, most of which do not produce significant changes in the heats of formation. It was observed, however, that for CaO and CaS the scalar relativistic corrections are unexpectedly large and highly basis set dependent. In these cases, Douglas-Kroll CCSD(T)/(aug-)cc-pWCV5Z calculations appear to give a converged result. The G3[CC](dir,full) and best W2C-type heats of formation are both found generally to agree well with experimental values recommended in recent critical compendia. However, in some cases (CaO, Ca(OH)2, and CaF2), they differ from one another by more than their predicted error margins. The available experimental data are not sufficiently precise to distinguish definitively between the two sets of results although, in general, when discrepancies exist the W2C heats of formation are lower in energy and tend to be in better agreement with experiment. In the case of CaO, the W2C heat of formation (20.7 kJ mol(-1)) is approximately 20 kJ mol(-1) lower than the G3[CC](dir, full) result and most of the experimental data. Extensive investigation of possible refinements of the W2C method has failed to reveal any weaknesses that could account for this discrepancy. We therefore believe that the heat of formation of CaO is likely to lie closer to the more recent direct experimental determination of 27 kJ mol(-1) than to the value of approximately 40 kJ mol(-1) recommended in recent thermochemical reviews.

We have studied the performance of dual basis (DB) sets for the evaluation of molecular properties via second order Møller-Plesset perturbation theory (MP2). In addition to savings derived from using a trimmed basis set for the underlying Hartree-Fock (HF) calculation, we pursued a systematic truncation of the virtual subspace for further reductions in computational overhead during the post-HF step. Calculated total energies and molecular properties within the DB framework without virtual space truncation are generally in excellent agreement with full basis calculations. When aug-cc-pV5Z is used as the parent basis, mean absolute error for DB-HF (DB-MP2) total energies of molecules within our test set is 9.7 × 10(-5) au (8.0 × 10(-5) au) while mean absolute relative errors for static electrical response properties like dipole moments, isotropic dipole polarizabilities and polarizability anisotropies are 0.15% (0.14%), 0.56% (0.72%), and 0.76% (0.83%) respectively. When DB is coupled with virtual space truncation at the MP2 level, the corresponding errors are larger but still within 2% of full basis values.

The adsorption energies and changes in surface work functions for benzene on unreconstructed Cu(111), Ag (111), and Au (111) at low coverages have been studied within the framework of dispersion corrected Kohn-Sham density functional theory. Corrections to account for long range dispersive effects between the adsorbate and metal substrate were incorporated via the exchange-hole dipole moment method of Becke and Johnson [J. Chem. Phys. 123, 154101 (2005)10.1063/1.2065267]. We show that the dispersion corrected calculations yield significantly improved adsorption energies and work function shifts that are in good agreement with experimental values.