Long-range Corrected Density Functional Theory Research Articles

Formation of Al + (C 6 H 6 ) 13 : The Origin of Magic Number in Metal–Benzene Clusters Determined by the Nature of the Core

The identification of highly abundant, “magic” species in the mass spectra of clusters have proven to be valuable in nanoscience, leading to the discovery of new stable species such as fullerenes a...

Organic Solar Cells Based on Non-fullerene Small-Molecule Acceptors: Impact of Substituent Position

Summary Molecular engineering of non-fullerene small-molecule acceptors (SMAs) plays a key role in enhancing the performance of organic solar cells. An effective strategy is to introduce functional groups into SMA end groups to tune the electronic and morphological properties of polymer/SMA blends. Here, molecular dynamics simulations and long-range corrected density functional theory calculations are combined to examine the impact of the position of methoxy substitution in the SMA end groups. As representative systems, blends of the IT-OM small-molecule acceptor with the PBDB-T polymer donor are explored; three different positions of the methoxy substitution of the IT-OM end groups are examined. By considering intermolecular mixing and packing, the energetic distribution of the charge-transfer electronic states, the exciton-dissociation and non-radiative recombination processes, and the electron-transfer rates among adjacent acceptors, we provide a comprehensive molecular-scale rationalization of the significant experimental variations in device performance for PBDB-T/IT-OM-based solar cells as a function of methoxy position.

Organic Solar Cells Based on Non-Fullerene Small-Molecule Acceptors: Impact of Substituent Position

Molecular engineering of non-fullerene small-molecule acceptors (SMAs) plays a key role in enhancing the performance of organic solar cells. An effective strategy is to introduce functional groups into SMA end-groups to tune the electronic and morphological properties of polymer/SMA blends. Here, molecular dynamics simulations and long-range corrected density functional theory calculations are combined to examine the impact of the position of methoxy substitution in the SMA end-groups. As representative systems, blends of the IT-OM small-molecule acceptor with the PBDB-T polymer donor are explored; three different positions of the methoxy substitution of the IT-OM end-groups are examined. By considering intermolecular mixing and packing, the energetic distribution of the charge-transfer electronic states, the exciton dissociation and nonradiative recombination processes, and the electron-transfer rates among adjacent acceptors, we provide a comprehensive molecular-scale rationalization of the significant experimental variations in device performance for PBDB-T/IT-OM-based solar cells as a function of methoxy position.

The Fragment Molecular Orbital Method Based on Long-Range Corrected Density-Functional Tight-Binding.

The presently available linear scaling approaches to density-functional tight-binding (DFTB) based on the fragment molecular orbital (FMO) method are severely impacted by the problem of artificial charge transfer due to the self-interaction error (SIE), which hampers the simulation of zwitterionic systems such as biopolymers or ionic liquids. Here we report an extension of FMO-DFTB where we included a long-range corrected (LC) functional designed to mitigate the DFTB SIE, called the FMO-LC-DFTB method, resulting in a robust method which succeeds in simulating zwitterionic systems. Both energy and analytic gradient are developed for the gas phase and the polarizable continuum model of solvation. The scaling of FMO-LC-DFTB with system size N is shown to be almost linear, O( N1.13-1.28), and its numerical accuracy is established for a variety of representative systems including neutral and charged polypeptides. It is shown that pair interaction energies between fragments for two mini-proteins are in excellent agreement with results from long-range corrected density functional theory. The new method was employed in long time scale (1 ns) molecular dynamics simulations of the tryptophan cage protein (PDB: 1L2Y ) in the gas phase for four different protonation states and in stochastic global minimum structure searches for 1-ethyl-3-methylimidazolium nitrate ionic liquid clusters containing up to 2300 atoms.

Insights into geometries, stabilities, electronic structures, reactivity descriptors, and magnetic properties of bimetallic Nim Cun-m (m = 1, 2; n = 3-13) clusters: Comparison with pure copper clusters.

A long-range corrected density functional theory (LC-DFT) was applied to study the geometric structures, relative stabilities, electronic structures, reactivity descriptors and magnetic properties of the bimetallic NiCun-1 and Ni2 Cun-2 (n = 3-13) clusters, obtained by doping one or two Ni atoms to the lowest energy structures of Cun , followed by geometry optimizations. The optimized geometries revealed that the lowest energy structures of the NiCun-1 and Ni2 Cun-2 clusters favor the Ni atom(s) situated at the most highly coordinated position of the host copper clusters. The averaged binding energy, the fragmentation energies and the second-order energy differences signified that the Ni doped clusters can continue to gain an energy during the growth process. The electronic structures revealed that the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies of the LC-DFT are reliable and can be used to predict the vertical ionization potential and the vertical electron affinity of the systems. The reactivity descriptors such as the chemical potential, chemical hardness and electrophilic power, and the reactivity principle such as the minimum polarizability principle are operative for characterizing and rationalizing the electronic structures of these clusters. Moreover, doping of Ni atoms into the copper clusters carry most of the total spin magnetic moment. © 2018 Wiley Periodicals, Inc.

Solvent effects and charge transfer states in organic photovoltaics: a time-dependent density functional theory study on the PCPDTBT:PCBM low band gap system

Long-range corrected time-dependent density functional theory has been used to study the solvent effect on excited state properties of PCPDTBT:PCBM (Poly[2,6-(4,4-dimethyl-4H-cyclopenta[2,1-b:3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]:[6,6]-Phenyl-C61-butyric acid methyl ester) molecular system. A polarizable continuum model has been applied within the linear response (LR) and state-specific (SS) approaches to account for the dielectric environment. The results show that the influence of the solvent depends on the nature of the excitations. For neutral excitonic states that are essentially localized on a single molecule, the solvent has little or no effects on the excitation energies according to both solvent schemes. On the other hand, for states with a significant amount of charge transfer (CT), the SS approach predicts a sufficient decline in the excitation energy as the dielectric constant increases so that the CT state can be stabilized to the lowest excited state, whereas the LR counterpart shows almost no change. The comparison of two solvent approaches is discussed.

Bulk Heterojunction Solar Cells: Impact of Minor Structural Modifications to the Polymer Backbone on the Polymer–Fullerene Mixing and Packing and on the Fullerene–Fullerene Connecting Network

AbstractThe morphology of the active layer of a bulk heterojunction solar cell, made of a blend of an electron‐donating polymer and an electron‐accepting fullerene derivative, is known to play a determining role in device performance. Here, a combination of molecular dynamics simulations and long‐range corrected density functional theory calculations is used to elucidate the molecular‐scale effects that even minor structural changes to the polymer backbone can have on the “local” morphology; this study focuses on the extent of polymer–fullerene mixing, on their packing, and on the characteristics of the fullerene–fullerene connecting network in the mixed regions, aspects that are difficult to access experimentally. Three representative polymer donors are investigated: (i) poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′″‐diyl)] (PffBT4T‐2OD); (ii) poly[(2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′″‐diyl)] (PBT4T‐2OD), where the fluorine atoms in the benzothiadiazole moieties of PffBT4T‐2OD are replaced with hydrogen atoms; and (iii) poly[(2,2′‐bithiophene)‐alt‐(4,7‐bis((2‐decyltetradecyl)thiophen‐2‐yl)‐5,6‐difluoro‐2‐propyl‐2H‐benzo[d][1,2,3]triazole)] (PT2‐FTAZ), where the sulfur atoms in the benzothiadiazole moieties of PffBT4T‐2OD are replaced with nitrogen atoms carrying a linear C3H7 side‐chain; these polymers are mixed with the phenyl‐C71‐butyric acid methyl ester (PC71BM) acceptor. This study also discusses the nature of the charge‐transfer electronic states appearing at the donor–acceptor interfaces, the electronic couplings relevant for the charge‐recombination process, and the electron‐transfer features between neighboring PC71BM molecules.

Theoretical Investigations on Proton Conductance and Degradation Mechanisms of Nafion Membrane in Fuel Cells

In this study, the low-humidity proton conductance and degradation mechanisms are theoretically investigated for Nafion®, which is the most frequently used proton exchange membrane. The proton conductance mechanism of Nafion membrane was first explored to reveal the cause for its high proton conductance under low-humidity conditions (Ref. 1). Nafion membrane gets an advantage in proton exchange membranes in fuel cells mainly due to its high low-humidity proton conductance. The actual proton conductance of Nafion at low humidity was explored by comparing to that of hydrocarbon multiblock sulfonated poly(arylene ether sulfone)s (SPE) membrane. Using long-range corrected density functional theory (LC-DFT) that one of the authors (TT) developed (Ref. 2), we calculated the proton dissociation energies from the sulfonic acid groups and investigated the subsequent proton conductance mechanism at low humidity. As a result, we found that these membranes have negligible difference in the proton dissociation ability inside the hydrated water clusters but show a remarkable difference in the conductivity of protonated water clusters in disconnected hydrogen bond networks. Note that low-humidity membranes are known to contain the regions of disconnected hydrogen bond networks (Ref. 3), in which Grotthuss mechanism assuming connected hydrogen bond networks does not proceed. Though vehicle mechanism assuming the diffusion of protonated water molecules (or clusters) seems to explain the proton conductance in the disconnected networks, we found that protonated water molecules and clusters need very large dissociation energies (about 400 kJ/mol). As an alternative, we suggested the relay mechanism (Fig. 1), in which protonated water clusters are relayed between the sulfonic acid groups through the doubly-hydrated structures. The calculated results showed that protonated water clusters require only about 100kJ/mol to dissociate in this relay mechanism. The vibrational spectra of hydrated Nafion membrane was also investigated to reveal the dependence of the proton conductance on humidity in further detail by a collaborative experimental and theoretical infrared (IR) spectroscopy study (Ref. 4). The experimental time-resolved attenuated total reflection Fourier transform IR spectroscopic results showed a unique IR peak intensity dependence on the hydration number. Based on the experimental results, we theoretically explored the dependence of the vibrational spectra of Nafion membrane on the hydration number by using LC-DFT. As a result, we found that this unique IR peak intensity dependence is correctly reproduced for the singly-hydrated but for the doubly-hydrated Nafion, in which protons are initially detached from the sulfonic acid groups in the geometry optimizations. This strongly supports the above-mentioned relay mechanism of the proton conductance. The degradation mechanism of Nafion membrane was also explored focusing on the H2O2-induced dissociation of the ether-linkages of the side chains. Many conventional studies on the degradation of membranes in fuel cells have assumed the principal mode of the degradation involves OH radicals. However, recent experimental studies have raised questions concerning this assumption. For example, a Fenton test, which is supposed to provide OH radicals, have revealed that the ratio of the degradation fragment molecules is considerably different from that of actual operating conditions (Ref. 5). Using LC-DFT, we found an H2O2-induced degradation mechanism, which is consistent with experimental results. In this mechanism, the ether-linkage of the side chains of Nafion is decomposed with a relatively low activation energy to produce (H2O)lHO3S-CF2-CF2-O-OH (l is the hydration number) as a key fragment. We also elucidated the subsequent decomposition reaction mechanisms, though these mechanism need metal ions to proceed. The vibrational spectra for the decomposed Nafion are found to be consistent with the experimental IR spectra. This mechanism is supposed to proceed together with OH radical-induced degradation mechanism. This work was supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cells (SPer-FC)” project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. T. Tsuneda, R. K. Singh, K. Miyatake, and M. Watanabe, Chem. Phys. Lett., 608, 11 (2014).H. Iikura, T. Tsuneda, T. Yanai, and K. Hirao, J. Chem. Phys., 115, 3540 (2001).G. Gebel, Polymer, 41, 5829 (2000); Macromolecules, 46, 6057 (2013).R. K. Singh, K. Kunimatsu, K. Miyatake, and T. Tsuneda, Macromolecules, 49, 6621 (2016).T. Kinumoto, M. Inaba, Y. Nakayama, K. Ogata, R. Umebayashi, A. Tasaka, Y. Iriyama, T. Abe, and Z. Ogumi, J. Pow. Sour., 158, 1222 (2006). Figure 1. Schematic diagram for the proton conductance in Nafion membrane in fuel cells. Figure 1

Interaction between anti-cancer drug hydroxycarbamide and boron nitride nanotube: A long-range corrected DFT study

An accurate long-range corrected density functional theory (CAM-B3LYP) is used to optimize hydroxycarbamide (HC) with pristine/Fe-doped boron nitride nanotubes (Fe-BNNTs). In order to investigate the more detailed mechanism of their interactions, Natural Bond Orbital (NBO), Quantum Theory of Atoms in Molecules (QTAIM), and Frontier Molecular Orbital (FMO) calculations are implemented. Weak interactions such as hydrogen bonds and Van der Waals’ dispersion are analyzed via the non-covalent interaction index (NCI) as well as the reduced density gradient (RDG) analyses. The molecular electrostatic potential and density of state spectra for all complexes are obtained. The local reactivity of the drug molecule is studied using the Fukui function. Adsorption energies in the gas phase and solution (via IEFPCM model) are also calculated. Based upon the results, all complexes are energetically favorable, especially in the aqueous phase. The calculated results showed that Fe doping in BNNT increases drug-nanotube interaction, especially in case Fe substitutes nitrogen atom.

Van der Waals DFT ONIOM study of the adsorption of DNA bases on the Cu(111) nanosurface

In this work, the adsorption of DNA bases on the Cu(111) nanosurface was studied to investigate the electronic structure of the bases on the Cu surface and to find the effect of van der Waals interactions on the adsorption mode of the bases. The calculations were performed in the ONIOM scheme using two DFT functionals (PW91PW91 and wB97XD). It was found that using the long-range corrected DFT functional such as wB97XD (which considers the vdW interactions) decreases the tilt angle of the bases on the surface. The main molecular orbitals responsible for the interaction and charge transfer between each base and Cu surface were determined. The HOMO-4, (HOMO, HOMO-2, and HOMO-3), (LUMO, HOMO-3, HOMO-4, and HOMO-6), and (LUMO and HOMO-4) are responsible for the interaction and charge transfer with the surface for adenine, cytosine, guanine, and thymine, respectively. The quantum theory of atoms in molecule (QTAIM) was used for better characterization of the interaction of the bases with the surface by a topological analysis of the electron density. The results showed that the most interacting atom of adenine with the Cu surface is the N atom of the NH2 group, whereas the most interacting atom of cytosine and guanine were the O atoms of the carbonyl groups. The QTAIM analysis also showed that the interaction of the O atom of cytosine with the Cu surface is stronger than that of guanine. For TY, the O and N atoms have higher interaction with the Cu surface compared to other atoms. Based on the calculated values of the electron density (ρBCP) and the positive sign of the Laplacian of the electron density (∇2ρBCP) at the bond critical points of the atom-atom interactions, it was concluded that the interaction between the bases and the surface can be categorized as closed-shell interactions.

Quantum Chemical Estimation of Acetone Physisorption on Graphene Using Combined Basis Set and Size Extrapolation Schemes

The physisorption of an acetone molecule on hexagonal graphene nanoflakes with increasing size has been investigated using a variety of quantum chemical methods capable of describing weak intermolecular interactions: coupled-cluster theory (CCSD and CCSD(T)), second-order Møller–Plesset perturbation theory with and without spin-component scaling (SCS-MP2 or standard MP2), long-range corrected density functional theory combined with a van der Waals functional (LC-BOP+ALL), meta-generalized gradient approximation functionals (M06-2X and M05-2X), and the dispersion augmented self-consistent-charge density functional tight-binding (SCC-DFTB-D) method. Our benchmark results for model systems as large as dicircumcoronene C96H24 have confirmed the suitability of the SCS-MP2 method for this specific system and the satisfactory performance of the computationally much more economical semiempirical SCC-DFTB-D method. The latter delivers a qualitatively accurate description of physisorption for flakes containing more than 800 carbon atoms. We predict accurate interaction energies of acetone with an infinitely large, defect-free graphene monolayer by combining extrapolation approaches for both increasing ab initio basis sets and graphene flake size in a two-dimensional extrapolation scheme.

Singularity Correction for Long-Range-Corrected Density Functional Theory with Plane-Wave Basis Sets

We introduced two methods to correct the singularity in the calculation of long-range Hartree-Fock (HF) exchange for long-range-corrected density functional theory (LC-DFT) calculations in plane-wave basis sets. The first method introduces an auxiliary function to cancel out the singularity. The second method introduces a truncated long-range Coulomb potential, which has no singularity. We assessed the introduced methods using the LC-BLYP functional by applying it to isolated systems of naphthalene and pyridine. We first compared the total energies and the HOMO energies of the singularity-corrected and uncorrected calculations and confirmed that singularity correction is essential for LC-DFT calculations using plane-wave basis sets. The LC-DFT calculation results converged rapidly with respect to the cell size as the other functionals, and their results were in good agreement with the calculated results obtained using Gaussian basis sets. LC-DFT succeeded in obtaining accurate orbital energies and excitation energies. We next applied LC-DFT with singularity correction methods to the electronic structure calculations of the extended systems, Si and SiC. We confirmed that singularity correction is important for calculations of extended systems as well. The calculation results of the valence and conduction bands by LC-BLYP showed good convergence with respect to the number of k points sampled. The introduced methods succeeded in overcoming the singularity problem in HF exchange calculation. We investigated the effect of the singularity correction on the excitation state calculation and found that careful treatment of the singularities is required compared to ground-state calculations. We finally examined the excitonic effect on the band gap of the extended systems. We calculated the excitation energies to the first excited state of the extended systems using a supercell model at the Γ point and found that the excitonic binding energy, supposed to be small for inorganic semiconductors, was quite large. Our findings suggest that more investigation on the effect of the excitonic binding energy on band gaps is necessary.

Nature of the Binding Interactions between Conjugated Polymer Chains and Fullerenes in Bulk Heterojunction Organic Solar Cells

Blends of π-conjugated polymers and fullerene derivatives are ubiquitous as the active layers of organic solar cells. However, a detailed understanding of the weak noncovalent interactions at the molecular level between the polymer chains and fullerenes is still lacking and could help in the design of more efficient photoactive layers. Here, using a combination of long-range corrected density functional theory calculations and molecular dynamic simulations, we report a thorough characterization of the nature of binding between fullerenes (C60 and PC61BM) and poly(benzo[1,2-b:4,5-b′]dithiophene–thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) chains. We illustrate the variations in binding strength when the fullerenes dock on the electron-rich vs electron-poor units of the polymer as well as the importance of the role played by the polymer and fullerene side chains and the orientations of the PC61BM molecules with respect to the polymer backbones.

Electronic excitation and injection of Ru-N3 dye anchored to TiO2 surface

A step-by-step theoretical protocol based on the density functional theory (DFT) and time-dependent DFT (TD-DFT) has been performed to study a Ruthenium polypyridyl complex named cis-dithiocyanatobis-(4,4′-dicarboxy-2,2′-bipyridine) ruthenium(II) (N3) sensitized TiO2 solar cell including dye excitations and electronic injection. Three binding structures of N3 anchored to a TiO2 nanoparticle (TiO2)38 have been adopted. The electronic structures and optical properties of N3 dye in gas phase, in solutions (with the explicit and implicit solvent models), and interfaced with TiO2 have been calculated. The hybrid DFT exchange-correlation (XC) functional B3LYP and PBE0, the newly-modified PBE0 functional PBE0-1/3, and the long-range corrected DFT (LRC-DFT) XC functional Cam-B3LYP have been applied. It is found that both the DFT XC functionals and molecular environments play a crucial role on molecular properties, which affect both the spectral lineshapes and peak positions. Coupled with PCM model, TD-PBE0-1/3 produces the best result compared with the experimental spectrum of N3 in CH2Cl2, TD-B3LYP slightly underestimates the excitation energies, and TD-Cam-B3LYP overestimates the excitation energies of 0.4–0.5eV. As the solvent polarity increases, the electronic absorption spectra of N3 dye blue shift. The absorption manners of N3 anchored to (TiO2)38 affect the electronic excitations, leading to different electronic injection pathways. Two of three anchoring manners favor the interfacial electronic transfer. In the end, three possible electronic injection pathways from the different parts of the excited dye to TiO2 nanoparticle have been suggested, indicating the different timescales of electron injections.

Refractive indices of organo-metallic and -metalloid compounds: A long-range corrected DFT study.

Refractive indices of metal- and metalloid-containing compounds are systematically evaluated using the Lorentz-Lorenz equation with polarizabilities obtained via density functional theory (DFT). Among exchange-correlation functionals studied, the long-range corrected (LC) fuctionals yield the lowest errors for the polarizabilities of gaseous compounds and refractive indices of liquids. The LC-DFT predicts very well the wavelength dependence of refractive indices. A scheme for computing Abbe numbers of organometallic and organometaloid compounds is proposed and a refractive index - Abbe number plot for 80 compounds is constructed. The compounds containing heavier metals tend to have higher refractive index and lower Abbe number, but several outliers, among them Te(CH3 )2 , Ni(PF3 )4 , Sb(C2 F3 )3 , Hg(C2 F3 )2 , are found. For Hg(C2 F3 )2 , also the effect of intramolecular and intermolecular degrees of freedom on polarizability is investigated. The absolute relative error in polarizability decreases from 5.7% for monomer model to 1.7% when a dimer model (derived from the available experimental crystal data) is employed. © 2016 Wiley Periodicals, Inc.

(Invited) Theoretical Investigation on Proton Conductance Mechanism in Proton Exchange Membranes

The hydrated structures of the proton exchange membranes were theoretically investigated using long-range corrected density functional theory [1,2] to make clear why perfluorinated polymer membrane Nafion is superior to other membranes in the proton conductivity at low humidity and consequently to reveal the proton conductance mechanism in low-humidity membranes, which are significant for anti-freezing. First, we compared the hydration structures of Nafion and multiblock sulfonated poly(arylene ether sulfone)s (SPE) hydrocarbon membranes for various hydration numbers. As a result, we found the relay mechanism of not protons but protonated water clusters between the sulfonic acid groups may contribute to the high proton conductivity of Nafion with less-hydrated sulfonic acid groups. In the relay mechanism (Fig.), protonated water clusters are relayed by the side chains through the doubly-hydrated sulfonic acid groups. We also examined the infrared (IR) spectrum calculations of Nafion to figure out its hydration structures at low humidity [4]. Consequently, we found that the experimental IR spectrum behaviour for various humidity conditions strongly supports the relay mechanism, because it is consistent only with the IR spectrum behaviour of the doubly-hydrated sulfonic acid groups, in which protons are detached beforehand. Based on the relay mechanism, we have also examined the proton conductance of state-of-the-art block co-polymer membranes that provide high proton conductance comparable to that of Nafion [5]: Sulfonated poly ketone (SPK) [6] and Sulfonated poly (p-phenylene) (SPP) [7] membranes. As a result, we found that these membranes have similar detachment abilities of protonated water clusters to that of Nafion, though they give slightly lower proton detachment abilities than that of Nafion. H. Iikura, T. Tsuneda, T. Yanai and K. Hirao, J. Chem. Phys. 115, 3540 (2001).T. Tsuneda, Density Functional Theory in Quantum Chemistry (Springer), (2014).R. K. Singh, T. Tsuneda, K. Miyatake and M. Watanabe, Chem. Phys. Lett. 608, 11 (2014).R. K. Singh, K. Kunimatsu, K. Miyatake, and T. Tsuneda, submitted.R. K. Singh, K. Miyatake, and T. Tsuneda, in preparation.T. Miyahara, T. Hayano, S. Matsuno, M. Watanabe, and K. Miyatake, ACS Appl. Mater. Interfaces 4, 2881 (2012).J. Miyake, T. Mochizuki and K. Miyatake, ACS Macro Lett. 4, 750 (2015). Figure 1

Photodissociation spectrum and structure of Au4+·H2O clusters

The gold–water interaction is essential for a fundamental understanding of the coordination chemistry of gold as well as applied materials sciences. Here isolated Au4+ and Au4+·H2O clusters are characterized with electronic photodissociation spectroscopy and long-range corrected time-dependent density functional theory. Structural information of these clusters is obtained by comparing their photodissociation spectra with the optical absorption spectra calculated for low-energy isomers, which are found with a genetic algorithm coupled to electronic structure methods. For Au4+, the most stable structure is found to be a D2h rhomboid, while a remarkable contribution of the higher-energy Y-shaped C2v isomer is also observed in the experimental spectrum. For Au4+·H2O, the most stable Cs (2A′) structure is formed through an AuO bond of H2O to the Au4+ (D2h) structure with a binding energy of 1.15eV. The Au4+·H2O structure exhibits Cs instead of C2v symmetry, which suggests substantial covalent contributions to the bonding between H2O and Au4+. The natural bond orbital charge analysis shows that a net positive charge of about 0.1e is transferred to H2O. The long-range corrected CAM-B3LYP* (ω=0.33) functional has proven reliable in predicting optical spectra of Au4+ and Au4+·H2O clusters close to experimental observation.

Molecular anions of polydeprotonated naphthalenes: An investigation on the metastability and deprotonation energies using nuclear-charge stabilization method.

The dianions and trianions of doubly- and triply-deprotonated naphthalenes are investigated using density functional theory (DFT) computations employing hybrid, long-range, and dispersion corrected exchange-correlation functionals. The investigated polyanionic species are found to be metastable with negative electron affinity and are further treated using a nuclear-charge stabilization method. The tunneling lifetimes of these anionic species were estimated to be a few femtoseconds. Notably, the deprotonated energies (DPEs) of naphthalene leading to the formation of triply deprotonated trianions are observed to be affected by the metastability of the dianions and trianions. For the deprotonation of doubly deprotonated dianions, the DPE calculated using the improved methodology based on the stabilization method is found to be nearly 100 kcal/mol more than that computed using the conventional procedure. Though the various DFT approximations employed are in a good agreement for predicting the lifetimes of the metastable species but in the prediction of electron-affinities and deprotonation energies, the dispersion-corrected DFT-D3 significantly disagrees with the long-range corrected DFT methods employing cam-B3LYP and ωB97XD exchange-correlation functionals.

Long-range corrected density functional theory with accelerated Hartree-Fock exchange integration using a two-Gaussian operator [LC-ωPBE(2Gau)

Since the advent of hybrid functional in 1993, it has become a main quantum chemical tool for the calculation of energies and properties of molecular systems. Following the introduction of long-range corrected hybrid scheme for density functional theory a decade later, the applicability of the hybrid functional has been further amplified due to the resulting increased performance on orbital energy, excitation energy, non-linear optical property, barrier height, and so on. Nevertheless, the high cost associated with the evaluation of Hartree-Fock (HF) exchange integrals remains a bottleneck for the broader and more active applications of hybrid functionals to large molecular and periodic systems. Here, we propose a very simple yet efficient method for the computation of long-range corrected hybrid scheme. It uses a modified two-Gaussian attenuating operator instead of the error function for the long-range HF exchange integral. As a result, the two-Gaussian HF operator, which mimics the shape of the error function operator, reduces computational time dramatically (e.g., about 14 times acceleration in C diamond calculation using periodic boundary condition) and enables lower scaling with system size, while maintaining the improved features of the long-range corrected density functional theory.

Semiclassical dynamics of electron attachment to guanine–cytosine base pair

Electron attachment dynamics to the guanine–cytosine (G–C) base pair in the gas phase is studied using DFT and molecular dynamics. The potential energy surface of the G–C anion is constructed with the empirical-valence-bond method using force-field information obtained from long-range corrected DFT calculations. Ring-polymer molecular dynamics simulations predict that the initial dipole-bound anion readily converts into the valence-bound anion within 0.1ps and proton-transfer occurs subsequently within 10ps. The same process was found in classical simulations, but on a much slower time scale. This result suggests that nuclear quantum effects are important in understanding DNA damage by low-energy electrons.