Three-body potential energy surface for parahydrogen

TL;DR

This paper develops a detailed three-body potential energy surface for para-hydrogen molecules using high-level ab initio calculations, revealing significant deviations from traditional models at short distances and improving the understanding of many-body interactions.

Contribution

The paper introduces a new, accurate three-body potential energy surface for para-hydrogen based on ab initio calculations, surpassing existing models in describing short-range interactions.

Findings

Deviations from Axilrod-Teller-Muto potential at short distances.

Configuration of three molecules in an equilateral triangle dominates interaction energy.

Modified ATM potential describes cases with two close molecules and one far away.

Abstract

We present a 3D isotropic ab initio three-body (para-H$_2$)$_3$ interaction potential energy surface (PES). The electronic structure calculations are carried out at the correlated coupled-cluster theory level, with single, double, and perturbative triple excitations. The calculations use an augmented correlation-consistent triple zeta basis set and a supplementary midbond function. We construct the PES using the Reproducing-Kernel Hilbert Space toolkit [J. Chem. Inf. Model. 57, 1923 (2017)] with phenomenological and empirical adjustments to account for short-range and long-range behaviour. The (para-H$_2$)$_3$ interaction energies deviate drastically from the Axilrod-Teller-Muto (ATM) potential at short intermolecular separations. We find that the configuration of three para-H$_2$ molecules at the corners of an equilateral triangle is responsible for the majority of the (para-H$_2$)$_3$ interaction energy contribution in a hexagonal-close-packed lattice. In cases where two para-H$_2$ molecules are close to one another while the third is far away, the (para-H$_2$)$_3$ interaction PES takes the form of a modified version of the ATM potential. We expect the combination of this PES together with a first principles para-H$_2$--para-H$_2$ Adiabatic Hindered Rotor potential to outperform a widely-used effective pair potential for condensed many-body systems of para-H$_2$.