Nonadiabatic spin dynamics in lanthanide complexes with the ab initio parametrized phenomenological Hamiltonian

Understanding the spin dynamics in paramagnetic lanthanide complexes is critical for developing molecular magnets and qubits with high blocking temperatures and long spin relaxation times. Because of the size and complexity of the electronic structure of metal complexes, most theoretical and computational efforts aimed at understanding their spin dynamics utilize different statistical methods. While these methods can predict experimentally measured quantities, the complete picture of spin dynamics, which is important for designing molecular magnets and qubits with desired properties, is often missing. We developed a new computational methodology based on the nonadiabatic molecular dynamics and the crystal field theory to simulate the spin relaxation in paramagnetic lanthanide complexes. This development includes 1) implementing the energy gradient and nonadiabatic (spin-vibrational) coupling for the crystal field theory, and 2) interfacing the crystal field theory with the ab initio multiple spawning (AIMS) molecular dynamics. The new nonadiabatic molecular dynamics provides unprecedented insight into the vibration-mediated transitions between different spin states of lanthanide complexes.