Slimmer Geminals For Accurate F12 Electronic Structure Models

TL;DR

This paper introduces optimized geminal parameters for higher-order F12 methods, significantly reducing basis set incompleteness errors in correlation energies and improving accuracy in energy calculations.

Contribution

It provides new geminal parameters tailored for higher-order F12 methods, enhancing their accuracy over previous parameters.

Findings

Reduced basis set incompleteness errors in correlation energies.

Significant improvements in atomization energies and ionization potentials.

Enhanced accuracy for high-order F12 electronic structure calculations.

Abstract

The Slater-type F12 geminal lengthscales originally tuned for the second-order M{\o}ller-Plesset F12 method are too large for higher-order F12 methods formulated using the SP (diagonal fixed-coefficient spin-adapted) F12 ansatz. The new geminal parameters reported herein reduce the basis set incompleteness errors (BSIE) of absolute coupled-cluster singles and doubles F12 correlation energies by a significant - and increasing with the cardinal number of the basis - margin. The effect of geminal reoptimization is especially pronounced for the cc-pVXZ-F12 basis sets (specifically designed for use with F12 methods) relative to their conventional aug-cc-pVXZ counterparts. The BSIEs of relative energies are less affected but substantial reductions can be obtained, especially for atomization energies and ionization potentials with the cc-pVXZ-F12 basis sets. The new geminal parameters are therefore recommended for all applications of high-order F12 methods, such as the coupled-cluster F12 methods and the transcorrelated F12 methods.