Electronic Structure and Decoherence in Optically Addressable Cr(IV)-based Magnetic Molecules*

Great success of point defects in wide-gap semiconductors for quantum information science applications stimulated extensive search for molecules with analogous properties. Recently, molecular spin states of a family of mononuclear Cr(IV)-based molecules have been shown to be initialized and read-out via optical transitions just like a deep nitrogen-vacancy defect in diamond. So far, decoherence mechanisms of the molecular spin states have not been discussed. Here, we investigate the electronic structure of the family of Cr(IV)-based molecules, by employing ab initio multireference quantum chemistry methods including spin-orbit coupling. We compute the excitation energy between the ground-state spin triplet and first-excited spin singlet as well as zero-field splitting of the triplet. Our results are compared to experimental data. As possible sources of spin decoherence, we calculate the magnetic hyperfine and nuclear quadrupole interaction parameters for the ⁵³Cr nucleus within the multireference methods. Furthermore, we study the interactions between the ligand ¹³C or ¹H nucleus and the molecular electronic spin for all ligand C and H sites of the molecules.