A CCSD(T)-based permutationally invariant polynomial 4-body potential for water

TL;DR

This paper develops a permutationally invariant polynomial potential energy surface for water's 4-body interactions, fitted to high-level CCSD(T) data, improving accuracy over previous models and validated through various tests.

Contribution

Introduces a new 4-body water potential energy surface based on CCSD(T) data, with rigorous dissociation limits and improved accuracy over existing models.

Findings

Better agreement with benchmark CCSD(T) results for water hexamer isomers.

Validated high-fidelity of the new potential through multiple tests.

Enhanced modeling of water interactions with a rigorous 4-body potential.

Abstract

We report a permutationally invariant polynomial (PIP) potential energy surface for the water 4-body interaction. This 12-atom PES is a fit to 2119, symmetry-unique, CCSD(T)-F12a/haTZ (aug-cc-pVTZ basis for 'O' atom and cc-pVTZ basis for 'H' atom) 4-b interaction energies. These come from low-level, direct-dynamics calculations, tetramer fragments from an MD water simulation at 300 K, and from the water hexamer, heptamer, decamer, and 13-mer clusters. The PIP basis is purified to ensure that the 4-b potential goes rigorously to zero in monomer+trimer and dimer+dimer dissociations for all possible such fragments. The 4-b energies of isomers of the hexamer calculated with the new surface are shown to be in better agreement with benchmark CCSD(T) results than those from the MB-pol potential. Other tests validate the high-fidelity of the PES.