A New Generation of Effective Core Potentials for Correlated Calculations

TL;DR

This paper proposes a new generation of effective core potentials (ECPs) designed for correlated calculations, improving transferability and accuracy in valence-only molecular simulations by incorporating correlated methods and better representation of core effects.

Contribution

It introduces a new approach to ECP construction that emphasizes correlated methods and transferability, achieving higher accuracy with fewer parameters.

Findings

Higher transferability accuracy than previous ECPs.

Enables many-body valence property calculations with comparable or better accuracy than all-electron methods.

Constructed ECPs incorporate effects of core-core and core-valence correlations.

Abstract

We outline ideas on desired properties for a new generation of effective core potentials (ECPs) that will allow valence-only calculations to reach the full potential offered by recent advances in many-body wave function methods. The key improvements include consistent use of correlated methods throughout ECP constructions and improved transferability as required for an accurate description of molecular systems over a range of geometries. The guiding principle is the isospectrality of all-electron and ECP Hamiltonians for a subset of valence states. We illustrate these concepts on a few first- and second-row atoms (B, C, N, O, S) and we obtain higher accuracy in transferability than previous constructions while using a semi-local ECPs with a small number of parameters. In addition, the constructed ECPs enable many-body calculations of valence properties with higher (or same) accuracy than their all-electron counterparts with uncorrelated cores. This implies that the ECPs include also some of the impacts of core-core and core-valence correlations on valence properties. The results open further prospects for ECP improvements and refinements.