The method of dispersion correction as an add-on to standard Kohn-Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C(6) coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/J%20Che%20Phy132,%20154104.pdf

A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu

"Chemists familiar with conventional quantum mechanics will applaud and benefit greatly from this particularly instructive, thorough and clearly written exposition of density functional theory: its basis, concepts, terms, implementation, and performance in diverse applications. Users of DFT for structure, energy, and molecular property computations, as well as reaction mechanism studies, are guided to the optimum choices of the most effective methods. Well done!" Paul von RaguE Schleyer "A conspicuous hole in the computational chemist's library is nicely filled by this book, which provides a wide-ranging and pragmatic view of the subject.[...It] should justifiably become the favorite text on the subject for practioneers who aim to use DFT to solve chemical problems." J. F. Stanton, J. Am. Chem. Soc. "The authors' aim is to guide the chemist through basic theoretical and related technical aspects of DFT at an easy-to-understand theoretical level. They succeed admirably." P. C. H. Mitchell, Appl. Organomet. Chem. "The authors have done an excellent service to the chemical community. [...] A Chemist's Guide to Density Functional Theory is exactly what the title suggests. It should be an invaluable source of insight and knowledge for many chemists using DFT approaches to solve chemical problems." M. Kaupp, Angew. Chem.

A Chemist's Guide to Density Functional Theory

Several modifications that have been made to the NDDO core-core interaction term and to the method of parameter optimization are described. These changes have resulted in a more complete parameter optimization, called PM6, which has, in turn, allowed 70 elements to be parameterized. The average unsigned error (AUE) between calculated and reference heats of formation for 4,492 species was 8.0 kcal mol−1. For the subset of 1,373 compounds involving only the elements H, C, N, O, F, P, S, Cl, and Br, the PM6 AUE was 4.4 kcal mol−1. The equivalent AUE for other methods were: RM1: 5.0, B3LYP 6–31G*: 5.2, PM5: 5.7, PM3: 6.3, HF 6–31G*: 7.4, and AM1: 10.0 kcal mol−1. Several long-standing faults in AM1 and PM3 have been corrected and significant improvements have been made in the prediction of geometries.

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Optimization of parameters for semiempirical methods V: modification of NDDO approximations and application to 70 elements.

In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.

Bond Dissociation Energies of Organic Molecules

A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Moller–Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr_2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.

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Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

I. Introduction and Scope 231A. Definitions of Atomic Electron Affinities 233B. Definitions of Molecular Electron Affinities 233II. Experimental Photoelectron Electron Affinities 235A. Historical Background 235B. The Photoeffect 236C. Experimental Methods 237D. Time-of-Flight Negative Ion PhotoelectronSpectroscopy239E. Some Thermochemical Uses of ElectronAffinities241F. Layout of Table 10: ExperimentalPhotoelectron Electron Affinities242III. Theoretical Determination of Electron Affinities 242A. Historical Background 2421. Theoretical Predictions of Atomic ElectronAffinities2422. Theoretical Predictions of MolecularElectron Affinities243B. Present Status of Theoretical Electron AffinityPredictions243C. Basis Sets and Theoretical Electron Affinities 244D. Density Functional Theory (DFT) andElectron Affinities245E. Layout of Tables 8 and 9: Theoretical DFTElectron Affinities247F. Details of Density Functional MethodsEmployed in Tables 8 and 9247IV. Discussion and Observations 248A. Statistical Analysis of DFT Results ThroughComparisons to Experiment and OtherTheoretical Methods248B. Theoretical EAs for Species with UnknownExperimental EAs251C. On the Applicability of DFT to Anions and theFuture of DFT EA Predictions251D. Specific Theoretical Successes 251E. Interesting Problems 2521. C

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Atomic and molecular electron affinities: photoelectron experiments and theoretical computations.

Ten stationary points on the water dimer potential energy surface have been characterized with the coupled-cluster technique which includes all single and double excitations as well as a perturbative approximation of triple excitations [CCSD(T)] Using a triple-ζ basis set with two sets of polarization functions augmented with higher angular momentum and diffuse functions [TZ2P(f,d)+dif], the fully optimized geometries and harmonic vibrational frequencies of these ten stationary points were determined at the CCSD(T) theoretical level In agreement with other ab initio investigations, only one of these ten stationary points is a true minimum Of the other nine structures, three are transition structures, and the remaining are higher order saddle points These high-level ab initio results indicate that the lowest lying transition state involved in hydrogen interchange is chiral, of C1 symmetry rather than Cs as suggested by recently developed 6D potential energy surfaces The one- and n-particle limits of t

Anchoring the water dimer potential energy surface with explicitly correlated computations and focal point analyses

MP2 and CCSD(T) complete basis set (CBS) limit relative electronic energies (DeltaE(e)) have been determined for eight low-lying structures of the water hexamer by combining explicitly correlated MP2-R12 computations with higher-order correlation corrections from CCSD(T) calculations. Higher-order correlation effects are quite substantial and increase DeltaE(e) by at least +0.19 kcal mol(-1) and as much as +0.59 kcal mol(-1). The effects from zero-point vibrational energy (ZPVE) have been assessed from unscaled harmonic vibrational frequencies computed at the MP2 level with a correlation consistent triple-zeta basis set (cc-pVTZ for H and aug-cc-pVTZ for O). ZPVE effects are even more significant than higher-order correlation effects and are uniformly negative, decreasing the relative energies by -0.16 kcal mol(-1) to -1.61 kcal mol(-1). Although it has been widely accepted that the cage becomes the lowest-energy structure after ZPVE effects are included [Nature 1996, 381, 501-503], the prism is consistently the most stable structure in this work, lying 0.06 kcal mol(-1) below the nearly isoenergetic cage isomer at the electronic MP2 CBS limit, 0.25 kcal mol(-1) below at the electronic CCSD(T) CBS limit, and 0.09 kcal mol(-1) below at the harmonic ZPVE corrected CCSD(T) CBS limit. Moreover, application of any uniform scaling factor less than unity to correct for anharmonicity further stabilizes the prism and increases the relative energies of the other structures.

CCSD(T) complete basis set limit relative energies for low-lying water hexamer structures.

Infrared cavity ringdown laser absorption spectroscopy has been used to study the O–H stretching vibrations of jet-cooled methanol clusters in direct absorption. Rovibrational bands for (CH3OH)2, (CH3OH)3, and (CH3OH)4 have been measured. Both bonded and free O–H stretches were measured for the dimer, indicating that its structure is linear. Five bands were assigned to the methanol trimer, indicating the presence of a second cyclic isomer in the molecular beam. A detailed study of the free O–H stretching region shows that methanol clusters larger than dimer must exist in cyclic ring configurations. In order to facilitate spectral assignment, harmonic frequencies and infrared intensities were calculated for the methanol monomer, dimer, and trimer with second order Mo/ller–Plesset perturbation theory. Using the theoretical infrared intensities and measured vibrational band absorptions, absolute cluster concentrations were calculated. Results agree with previous experimental and theoretical work.

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Infrared cavity ringdown spectroscopy of methanol clusters: Single donor hydrogen bonding

The atomic electron affinities of the eight first row (H,Li,…,F) atoms as well as the adiabatic electron affinities of 12 first row diatomic and 15 first row triatomic molecules were determined using six different density functional or hybrid Hartree–Fock/density functional methods. The 35 species were selected for having relatively well-established experimental electron affinities. Harmonic zero-point vibrational energy corrected electron affinities are also reported for the diatomic and triatomic molecules. Equilibrium geometries and harmonic vibrational frequencies are given for the 27 molecules and their anions as determined with each density functional method. Discussion focuses on comparison of theoretical and experimental electron affinities. For the atomic, diatomic, and triatomic electron affinities the average absolute error is reported for each exchange–correlation functional. Since many of the molecular anion structures and vibrational frequencies are unknown, the work suggests new experimental directions.

Gregory S. Tschumper

Papers

Atomic and molecular electron affinities: photoelectron experiments and theoretical computations.

Anchoring the water dimer potential energy surface with explicitly correlated computations and focal point analyses

CCSD(T) complete basis set limit relative energies for low-lying water hexamer structures.

Infrared cavity ringdown spectroscopy of methanol clusters: Single donor hydrogen bonding

Predicting electron affinities with density functional theory: some positive results for negative ions