Blind test of density-functional-based methods on intermolecular interaction energies

In the past decade, a number of approaches have been developed to fix the failure of (semi) local density-functional theory (DFT) in describing intermolecular interactions. The performance of several such approaches with respect to highly accurate benchmarks is compared here on a set of separation-dependent interaction energies for ten dimers. Since the benchmarks were unknown before the DFT-based results were collected, this comparison constitutes a blind test of these methods

Many-body dispersion corrections for periodic systems: an efficient reciprocal space implementation

International audienceThe energy and gradient expressions for the many-body dispersion scheme (MBD@rsSCS) of Ambrosetti et al (2014 J. Chem. Phys. 140 18A508) needed for an efficient implementation of the method for systems under periodic boundary conditions are reported. The energy is expressed as a sum of contributions from points sampled in the first Brillouin zone, in close analogy with planewave implementations of the RPA method for electrons in the dielectric matrix formulation. By avoiding the handling of large supercells, considerable computational savings can be achieved for materials with small and medium sized unit cells. The new implementation has been tested and used for geometry optimization and energy calculations of inorganic and molecular crystals, and layered materials

Tkatchenko-Scheffler van der Waals correction method with and without self-consistent screening applied to solids

International audienceThe method proposed by Tkatchenko and Scheffler [Phys. Rev. Lett. 102, 073005 (2009)] to correct density functional calculations for the missing van derWaals interactions is implemented in the Vienna ab initio simulation package (VASP) code and tested on a wide range of solids, including noble-gas crystals, molecular crystals (alpha-N-2, sulfur dioxide, benzene, naphthalene, cytosine), layered solids (graphite, hexagonal boron nitride, vanadium pentoxide, MoS2, NbSe2), chain-like structures (selenium, tellurium, cellulose I), ionic crystals (NaCl, KI), and metals (nickel, zinc, cadmium). In addition to the original formulation expressing the van der Waals (vdW) corrections as pairwise potentials whose strength is derived from the rescaled polarizabilities of the neutral free atoms, the self-consistently screened (TS + SCS) [Phys. Rev. Lett. 108, 236402 (2012)] variant of the method involving electrodynamic response effects has been examined. Analytical expressions for the forces acting on the atoms and for the components of the stress tensor needed for the relaxation of the volume and shape of the unit cell using the TS + SCS method are derived. While the calculated structures are reasonably close to experiment, the van der Waals corrections to the binding energies are often found to be overestimated in comparison with experimental data. The TS + SCS approach leads to significantly better results in some problematic cases, such as the binding energy of graphite. However, there is room for further improvements, in particular for strongly ionic systems

Does the Exchange-Correlation Kernel ƒxc Have a Very Long-Ranged Dependence on the Groundstate Electron Density?

We consider the dispersion energy between two well-separated molecules. Provided that exchange overlap effects can be neglected, the Generalized Casimir Polder (GCP) formula gives the dispersion energy exactly to second order in the inter-system Coulomb pair potential, in terms of the density response functions of the isolated molecules. One can alternatively calculate the dispersion interaction from the density response in a supramolecular (dimer) energy TDDFT/ACFD calculation. This uses the density response from Time Dependent Density Functional Theory (TDDFT) and the Adiabatic Connection (ACFD) groundtstate electronic energy formula, and treats the two systems together. Some of us recently [JCTC 13, 5829 (2017)] showed that the supramolecular TDDFT/ACFD approach can fail to reproduce the exact GCP result, when the exchange-correlation kernel ƒxc in the TDDFT calculation is assumed to be local. Here we examine ways in which a nonlocal density dependence of ƒxc might be able to remove this discrepancy. <br

An efficient method for the coordinate transformation problem of massively three-dimensional networks

Theme 4 - Simulation et optimisation de systemes complexes - Projet NumathAvailable from INIST (FR), Document Supply Service, under shelf-number : 14802 E, issue : a.2000 n.4083 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc