Relativistic coupled cluster with completely renormalized and perturbative triples corrections

TL;DR

This paper implements noniterative triples corrections within a relativistic coupled-cluster framework to accurately compute properties of heavy metal dimers, highlighting the importance of relativistic effects and triples excitations.

Contribution

It introduces a noniterative triples correction method within the 1eX2C relativistic CC framework and demonstrates its effectiveness on heavy metal dimers.

Findings

Relativistic effects and triples corrections significantly influence dissociation energies.

Spin-orbit coupling is crucial for accurate potential energy curves.

Relativistic effects are more pronounced in gold dimers than in silver or copper.

Abstract

We have implemented noniterative triples corrections to the energy from coupled-cluster with single and double excitations (CCSD) within the 1-electron exact two-component (1eX2C) relativistic framework. The effectiveness of both the CCSD(T) and the completely renormalized (CR) CC(2,3) approaches are demonstrated by performing all-electron computations of the potential energy curves and spectroscopic constants of copper, silver, and gold dimers in their ground electronic states. Spin-orbit coupling effects captured via the 1eX2C framework are shown to be crucial for recovering the correct shape of the potential energy curves, and the correlation effects due to triples in these systems changes the dissociation energies by about 0.1--0.2 eV or about 4--7\%. We also demonstrate that relativistic effects and basis set size and contraction scheme are significantly more important in Au$_2$ than in Ag$_2$ or Cu$_2$.