The goal of this project is to apply correlated, relativistic many-body quantum chemistry methods to challenging problems in chemistry where spin-dependent effects cannot be ignored. In particular, relativistic equation-of-motion coupled-cluster (EOM-CC) approaches will be applied to Fe(II)-based spin-crossover compounds and Ni(II)-based single-molecule magnets (SMMs), which have potential applications as components in novel magnetic materials and in quantum information science. For the spin-crossover complexes, ligand-field splitings and spin-transition temperatures will be derived from electron atachment (EA) EOM-CC calculations applied to the (N-1)-electron state of the Fe(II) complex (wherein the metal center has an easy-to-describe 3d5 configuration). For the SMMs, magnetic anisotropy parameters will be derived from double ionization potential (DIP) EOM-CC theory applied to the (N+2)-electron state of Ni(II) (wherein the metal center has a similarly easy-to-describe 3d10 configuration). Relativistic CC with up to (perturbative) triple excitations will also be applied to lanthanide oxide molecules, the electronic structure of which can provide insights into larger lanthanide-containing SMMs.
Broadly, this research aims to address a growing need in the computational chemical sciences for accurate first-principles descriptions of the relativistic quantum dynamics of many-electron systems. This need is driven by emerging quantum technologies that are increasingly important in material design, as scientists and engineers seek to manipulate spins toward a variety of goals, including novel magnetic materials and quantum information science (using spin-based molecular qubits, for example). Fundamental to these scientific and technological applications are the correlated many-electron dynamics of systems driven far from equilibrium, the accurate and efficient description of which represents a grand outstanding challenge in computational chemistry, especially when considering spin-dependent processes (e.g., spin-coherence, spin-entanglement, intersystem crossing, etc.)