Spherical harmonics representation of the potential energy surface for the H2⋯H2 van der Waals complex

Abstract

We perform a study of the molecular anisotropy for the H 2 • • • H 2 van der Waals system using a spherical harmonics expansion. We use six leading stable configurations to construct our analytical potential energy surface (PES) from ab initio calculations guided qualitatively by the symmetry-adapted perturbation theory (SAPT) analyses. We extrapolate the energies of the PES performed at the CCSD(T)/aug-cc-pVnZ (n = 2 and 3) levels to the complete basis set (CBS) limit. To best fit the shallow potential energy surface of each leading configuration with the intermolecular distance, it was employed an extended version of the Rydberg potential. To assess the quality of our extrapolated analytical PES, we calculate the second virial coefficients, which are in relatively good agreement with the experimental data. As a result, the spherical harmonics coefficients obtained might be of considerable relevance in spectroscopy and dynamics applications. Keywords Symmetry-adapted perturbation theory • Potential energy surface • Van der Waals complex • Spherical harmonics • Second virial coefficient This paper belongs to Topical Collection XX-Brazilian Symposium of Theoretical Chemistry (SBQT2019)

van der Waals Radii of Free and Bonded Atoms From Hydrogen (Z=1) to Oganesson (Z=118)

“…24,[73][74][75][76] However, several specific configurations exist where the intramolecular structure of two hydrogen molecules is conserved, and the binding of the two monomers is dominated by vdW forces. 74,77 For this study, we have selected the collinear, parallel, perpendicular, and shifted parallel configurations (see Figure 4), given that previous SAPT analyses indicate that their equilibrium geometry is caused by a balance between exchange and dispersion interactions.…”