Multiconfiguration Pair-Density Functional Theory for Chromium(IV) Molecular Qubits.

Area of Science:

• Quantum computing
• Materials science
• Computational chemistry

Background:

• Pseudotetrahedral organometallic complexes with chromium(IV) and aryl ligands are emerging as potential molecular qubit candidates.
• Accurate computation of electronic properties is crucial for designing and optimizing molecular qubits.

Purpose of the Study:

• To develop and validate a computational protocol for calculating singlet-triplet gaps and zero-field splitting (ZFS) parameters in Cr(IV) aryl complexes.
• To assess the performance of multireference methods compared to standard density functional theory for these properties.

Main Methods:

• Multiconfiguration pair-density functional theory (PDFT) was employed.
• Two multireference methods, multistate complete active space second-order perturbation theory (MS-CASPT2) and hybrid multistate pair-density functional theory (HMS-PDFT), were utilized.
• Calculations investigated the dependence on active space and molecular geometry.

Main Results:

• MS-CASPT2 and HMS-PDFT demonstrated superior accuracy for singlet-triplet gaps compared to Kohn-Sham density functional theory.
• Both multireference methods showed good qualitative agreement for the very small ZFS parameters.
• The methods accurately predicted the trend in the ratio of rhombic and axial ZFS parameters (|E/D|).

Conclusions:

• The developed computational protocol, particularly using MS-CASPT2 and HMS-PDFT, is effective for predicting key properties of molecular qubit candidates.
• These methodologies provide a reliable guide for future computational studies of ZFS parameters in novel molecular qubit designs.