Zero-Field Splitting Calculations by Multiconfiguration Pair-Density Functional Theory

Zero-field splitting (ZFS) is a fundamental molecular property that is especially relevant for single-molecule magnets (SMMs), electron paramagneticresonance spectra, and quantum computing. Developing a method that can accuratelypredict ZFS parameters can be very powerful for designing new SMMs. One of thechallenges is to include external correlation in an inherently multiconfigurationalopen-shell species for the accurate prediction of magnetic properties. Previouslyavailable methods depend on expensive multireference perturbation theorycalculations to include external correlation. In this paper, we present spin-orbit-inclusive multiconfiguration and multistate pair-density functional theory (MC-PDFT) calculations of ZFSs; these calculations have a cost comparable to complete-active-space self-consistentfield (CASSCF) theory, but they include correlation external to the active space. We found that combining a multistate formulation of MC-PDFT, namely, compressed-state multistate pair-density functional theory, with orbitals optimized by weighted-state-averaged CASSCF, yields reasonably accurate ZFS results

Automated summary

Zero-field splitting (ZFS) is a fundamental molecular property that is important for various applications. Predicting ZFS parameters accurately requires addressing the challenge of including external correlation. This paper presents a cost-effective method, MC-PDFT, which combines spin-orbit-inclusive multiconfiguration and multistate pair-density functional theory, to accurately calculate ZFS.