It is shown by an extensive benchmark on molecular energy data that the mathematical form of the damping function in DFT-D methods has only a minor impact on the quality of the results. For 12 different functionals, a standard "zero-damping" formula and rational damping to finite values for small interatomic distances according to Becke and Johnson (BJ-damping) has been tested. The same (DFT-D3) scheme for the computation of the dispersion coefficients is used. The BJ-damping requires one fit parameter more for each functional (three instead of two) but has the advantage of avoiding repulsive interatomic forces at shorter distances. With BJ-damping better results for nonbonded distances and more clear effects of intramolecular dispersion in four representative molecular structures are found. For the noncovalently-bonded structures in the S22 set, both schemes lead to very similar intermolecular distances. For noncovalent interaction energies BJ-damping performs slightly better but both variants can be recommended in general. The exception to this is Hartree-Fock that can be recommended only in the BJ-variant and which is then close to the accuracy of corrected GGAs for non-covalent interactions. According to the thermodynamic benchmarks BJ-damping is more accurate especially for medium-range electron correlation problems and only small and practically insignificant double-counting effects are observed. It seems to provide a physically correct short-range behavior of correlation/dispersion even with unmodified standard functionals. In any case, the differences between the two methods are much smaller than the overall dispersion effect and often also smaller than the influence of the underlying density functional.

Effect of the damping function in dispersion corrected density functional theory

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software

/pdf/advanced-capabilities-for-materials-modelling-with-quantum-40poaosrve.pdf

Advanced capabilities for materials modelling with Quantum ESPRESSO.

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

/pdf/advanced-capabilities-for-materials-modelling-with-quantum-1mm65lmkt8.pdf

Advanced capabilities for materials modelling with Quantum ESPRESSO

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.

/pdf/advances-in-molecular-quantum-chemistry-contained-in-the-q-3j7dwbtpjv.pdf

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

The Atomic Simulation Environment (ASE) is a software package written in the Python programming language with the aim of setting up, steering, and analyzing atomistic simula- tions. In ASE, tasks are fully scripted in Python. The powerful syntax of Python combined with the NumPy array library make it possible to perform very complex simulation tasks. For example, a sequence of calculations may be performed with the use of a simple "for-loop" construction. Calculations of energy, forces, stresses and other quantities are performed through interfaces to many external electronic structure codes or force fields using a uniform interface. On top of this calculator interface, ASE provides modules for performing many standard simulation tasks such as structure optimization, molecular dynamics, handling of constraints and performing nudged elastic band calculations.

/pdf/the-atomic-simulation-environment-a-python-library-for-48jb1pkf0e.pdf

The Atomic Simulation Environment - A Python library for working with atoms

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

We reinvestigate the performance of Kohn–Sham density functional (DF) methods for a thermochemical test set of bond separation reactions of alkanes (BSR36) published recently by Steinmann et al. [J. Chem. Theory Comput. 5, 2950 (2009)]. According to our results, the tested approximations perform for this rather special benchmark as usual. We show that the choice of reference enthalpies plays a crucial role in the assessment. Due to the large stoichiometric factors involved, errors of various origin are strongly amplified. Inconsistent reference data are avoided by computing reference energies at the CCSD(T)/CBS level. These are compared to results for a variety of standard DFs. Two different versions of London dispersion corrections (DFT-D2 and DFT-D3) are applied and found to be very significant. The most accurate results are obtained with B2GPPLYP-D2 (MAD = 0.4 kcal mol−1) B2PLYP-D2 (MAD = 0.5 kcal mol−1) and B97-D2 (MAD = 0.9 kcal mol−1 methods. Dispersion corrections not only improve the computed BSR ...

/pdf/thermochemical-benchmarking-of-hydrocarbon-bond-separation-5bkz8osass.pdf

Thermochemical benchmarking of hydrocarbon bond separation reaction energies: Jacob's ladder is not reversed!

We reinvestigate the performance of Kohn-Sham density functional (DF) methods for a thermochemical test set of bond separation reactions of alkanes (BSR36) published recently by Steinmann et al (J. Chem. Theory Comput. 2009, 5, 2950). According to our results, the tested approximations perform for this rather special benchmark as usual. We show that the choice of reference enthalpies plays a crucial role in the assessment. Due to the large stoichiometric factors involved, errors of various origin are strongly amplified. Inconsistent reference data are avoided by computing reference energies at the CCSD(T)/CBS level. These are compared to results for a variety of standard DFs. Two different versions of London dispersion corrections (DFT-D2 and DFT-D3) are applied and found to be very significant. The most

RESEARCH ARTICLE Thermochemical benchmarking of hydrocarbon bond separation reaction energies: Jacob's ladder is not reversed!

Microporous organic molecular crystals (MOMCs) are materials composed of discrete organic molecules interacting noncovalently. The gas uptake of CO2, CH4, N2, and Xe in one of the most widely investigated MOMCs, trispiro(benzodioxole[2′.2:2″.4:2‴.6]1,3,5,2,4,6-triazatriphosphinine) (1), was computed by grand canonical Monte Carlo (GCMC) simulations based on our lately developed force field method vdW3, which is fitted to accurate ab initio potentials (double hybrid functional B2PLYP with a D3 dispersion correction using def2-TZVPP basis sets). The B2PLYP-D3 results compare very well with CCSD(T)/CBS interaction energies for benzene–gas model complexes. Our multiscale modeling approach to accurate interaction potentials is found to be essential in order to obtain reasonable adsorption isotherms and heats of adsorption. The good agreement between the simulation results and experimental data in all cases gives us the opportunity to design novel complex materials for gas adsorption based solely on first-princ...

Helge Krieg

Papers

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

Thermochemical benchmarking of hydrocarbon bond separation reaction energies: Jacob's ladder is not reversed!

RESEARCH ARTICLE Thermochemical benchmarking of hydrocarbon bond separation reaction energies: Jacob's ladder is not reversed!

Accurate Computation of Gas Uptake in Microporous Organic Molecular Crystals