title: Evaluating dispersion forces for optimization of van der Waals complexes using a non-empirical functional.
abstract: Modelling dispersion interactions with traditional density functional theory (DFT) is a challenge that has been extensively addressed in the past decade. The exchange-dipole moment (XDM), among others, is a non-empirical add-on dispersion correction model in DFT. The functional PW86+PBE+XDM for exchange, correlation and dispersion, respectively, compromises an accurate functional for thermochemistry and for van der Waals (vdW) complexes at equilibrium and non-equilibrium geometries. To use this functional in optimizing vdW complexes, rather than computing single point energies, it is necessary to evaluate accurate forces. The purpose of this paper is to validate that, along the potential energy surface, the distance at which the energy is minimum is commensurate with the distance at which the forces vanish to zero. This test was validated for 10 rare gas diatomic molecules using various integration grids and different convergence criteria. It was found that the use of either convergence criterion, 10-6or 10-8, in Gaussian09, does not affect the accuracy of computed optimal distances and binding energies. An ultra-fine grid needs to be used when computing accurate energies using generalized gradient approximation functionals.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.
authors.affiliation: College of Natural and Health Sciences, Zayed University, Abu Dhabi, PO Box 144534, United Arab Emirates alya.arabi@zu.ac.ae.
authors.forename: Alya A
authors.identifier: http://orcid.org/0000-0003-3664-314X
authors.initials: AA
authors.lastname: Arabi
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D005740:Gases / Q000737:chemistry* / Q000528:radiation effects; D008956:Models, Chemical; D015233:Models, Statistical; D055672:Static Electricity; D013314:Stress, Mechanical
chemical_list: D005740:Gases
keywords: computing forces; density functional theory; dispersion interactions; exchange-hole dipole moment model; van der Waals complexes