The convergence of the ab-initio many-body expansion for the cohesive energy of solid mercury

TL;DR

This paper investigates the convergence issues of many-body expansions for solid mercury's cohesive energy and proposes an embedded cluster approach that yields results matching experimental data.

Contribution

The study introduces an incremental embedded cluster method that significantly improves the convergence of many-body expansions for solid mercury.

Findings

Conventional many-body expansions show poor convergence for mercury clusters.

The embedded cluster approach enhances convergence and accuracy.

Calculated cohesive energy matches experimental value of 0.79 eV.

Abstract

A many-body expansion for mercury clusters of the form E = \sum_{i<j}\Delta \epsilon_{ij} + \sum_{i<j<k}\Delta \epsilon_{ijk} + ... \quad, does not converge smoothly with increasing cluster size towards the solid state. Even for smaller cluster sizes (up to n=6), where van der Waals forces still dominate, one observes bad convergence behaviour. For solid mercury the convergence of the many-body expansion can dramatically be improved by an incremental procedure within an embedded cluster approach. Here one adds the coupled cluster many-body electron correlation contributions of the embedded cluster to the bulk HF energy. In this way we obtain a cohesive energy (not corrected for zero-point vibration) of 0.79 eV in perfect agreement with the experimental value.