On the basis set selection for calculations of core-level states: different strategies to balance cost and accuracy

Abstract

We present a study on basis set effects in correlated calculations of core-level states. While it is well recognised that the core-level states require using more extensive basis sets than their valence counterparts, the standard strategy has been to use large contracted basis sets, such as the cc-pVXZ or cc-pCVXZ series. Building upon the ideas of Besley et al. [J. Chem. Phys. 130, 124308 (2009)], we show that a much more effective strategy is to use uncontracted bases, such as core or fully uncontracted Pople's basis. The physical grounds behind this approach are explained and illustrated by numeric results. We also discuss other cost-saving strategies, such as virtual space truncation and mixed precision execution.

GRAPHICAL ABSTRACT

KEYWORDS:

• Benchmark
• core ionized states
• coupled cluster theory
• basis set selection
• core-valence separation
• contracted basis sets

Acknowledgments

We are grateful to Prof. Peter Gill from the University of Sydney for his insightful remarks on the physics of core-ionised states and anticipated consequences for basis set selection, which motivated the present study.

Disclosure statement

A.I.K. is the President and a part-owner of Q-Chem, Inc.

Additional information

Funding

This work was supported by the U.S. National Science Foundation (No. CHE-1856342). A.I.K. is a grateful recipient of the Simons Fellowship in Theoretical Physics and Mildred Dresselhaus Award from CFEL/DESY, which supported her sabbatical stay in Germany. M.L.V. and S.C. acknowledge financial support from DTU Chemistry - Department of Chemistry, Technical University of Denmark and from the Independent Research Fund Denmark–Natural Sciences, DFF-RP2 grant no. 7014-00258B. S.C. also acknowledges the European Union's Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie Grant Agreement No. 765739, ‘COSINE- European Training Network on Computational Spectroscopy In Natural sciences and Engineering’.