Molecular magnets have potential applications in quantum computing, data storage, and spintronics due to their unique spin properties. Understanding the interplay between spin and phonon degrees of freedom and the phonon assisted spin relaxation dynamics in these systems is essential for to exploit their full potential. In this work we present a theoretical exploration of spin-phonon relaxation dynamics in a lanthanide-based single molecule magnet (SMM) namely [Dy(acac)3(H2O)2].EtOH.H2O¹. To capture the strongly correlated electronic states inherent in f-elements (lanthanides), multireference methods, such as complete active space self-consistent field (CASSCF) are essential. However, the CASSCF method cannot adequately capture the dynamic correlation outside the active space which is crucial to accurately describe the quantum states involved in spin transitions. The magnetic properties of single molecule magnets SMM can significantly change due to the incorporation of dynamic electron correlation, which in turn impacts the spin relaxation rate. The interplay between the strong spin-orbit coupling and dynamic electron correlation in the Dy³⁺ ion has been shown in literature to have significant effects on the energy splitting between different total angular momentum (M_J) states.² Here we use a post-CASSCF method namely multiconfiguration pair-density functional theory (MC-PDFT)³, that combines the CASSCF wave function with a functional of the electron density and on-top pair density. The method provides a correction of the CASSCF energies with similar accuracy of perturbative approaches such as CASPT2, but at significantly lower computational cost. We use a supercell model to compute the phonon modes using the periodic density functional theory. The spin phonon coupling is then computed via mapping the MC-PDFT electronic structures onto a model crystal field Hamiltonian. We then perform quantum mechanical first principles spin-dynamics simulations to calculate spin-phonon relaxation rates and study their dependence on various parameters, including temperature and external fields. This is the first implementation and application of MC-PDFT for spin-phonon dynamics.

Soumi Haldar

Appearances