Application of the multireference equation of motion coupled cluster method, including spin–orbit coupling, to the atomic spectra of Cr, Mn, Fe and Co

Abstract

The recently introduced multireference equation of motion (MR-EOM) approach is combined with a simple treatment of spin–orbit coupling, as implemented in the ORCA program. The resulting multireference equation of motion spin–orbit coupling (MR-EOM-SOC) approach is applied to the first-row transition metal atoms Cr, Mn, Fe and Co, for which experimental data are readily available. Using the MR-EOM-SOC approach, the splittings in each L-S multiplet can be accurately assessed (root mean square (RMS) errors of about 70 cm⁻¹). The RMS errors for J-specific excitation energies range from 414 to 783 cm⁻¹ and are comparable to previously reported J-averaged MR-EOM results using the ACESII program. The MR-EOM approach is highly efficient. A typical MR-EOM calculation of a full spin–orbit spectrum takes about 2 CPU hours on a single processor of a 12-core node, consisting of Intel XEON 2.93 GHz CPUs with 12.3 MB of shared cache memory.

Keywords:

• atomic excited states
• coupled cluster
• spin–orbit coupling
• equation of motion coupled cluster

Acknowledgements

This work has been supported by the Natural Sciences and Engineering Research Council (NSERC) through a discovery grant to M. Nooijen and a Vanier Canada Graduate Scholarship to L.M.J. Huntington. It is our pleasure to present this work in the special issue on the occasion of the 60th birthday of Prof. Sourav Pal.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00268976.2015.1063730.

Additional information

Funding

M. Nooijen: Natural Sciences and Engineering Research Council (NSERC)