A new generation of effective core potentials from correlated and spin-orbit calculations: selected heavy elements

TL;DR

This paper develops new correlation consistent effective core potentials (ccECPs) for several heavy elements, improving accuracy in valence calculations by incorporating spin-orbit effects and systematic refinements, validated through molecular and quantum Monte Carlo tests.

Contribution

Introduction of systematically optimized ccECPs for heavy elements that include spin-orbit effects, enhancing transferability and accuracy over previous ECPs.

Findings

ccECPs outperform previous ECPs on all tested criteria

Inclusion of AREP part is crucial for ECP quality

Accurate trial wave functions are essential for quantum Monte Carlo calculations

Abstract

We introduce new correlation consistent effective core potentials (ccECPs) for the elements I, Te, Bi, Ag, Au, Pd, Ir, Mo, and W with $4d$, $5d$, $6s$ and $6p$ valence spaces. These ccECPs are given as a sum of spin-orbit averaged relativistic effective potential (AREP) and effective spin-orbit (SO) terms. The construction involves several steps with increasing refinements from more simple to fully correlated methods. The optimizations are carried out with objective functions that include weighted many-body atomic spectra, norm-conservation criteria, and spin-orbit splittings. Transferability tests involve molecular binding curves of corresponding hydride and oxide dimers. The constructed ccECPs are systematically better and in a few cases on par with previous effective core potential (ECP) tables on all tested criteria and provide a significant increase in accuracy for valence-only calculations with these elements. Our study confirms the importance of the AREP part in determining the overall quality of the ECP even in the presence of sizable spin-orbit effects. The subsequent quantum Monte Carlo (QMC) calculations point out the importance of accurate trial wave functions which in some cases (mid series transition elements) require treatment well beyond single-reference.