Toward Better Understanding of Molecular Magnetic Properties with ab initio Simulation Methods

Abstract

Simulating and understanding magnetic properties are essential for developing new magnetic materials. In this dissertation, some advances in ab initio methodologies for simulating magnetic properties based on the variational treatment of magnetic fields are presented. The new methodologies are applied for properties such as noncollinear spin and magnetic circular dichroism (MCD), and bring further insights into these phenomena. In Chapter 1, we give a general introduction of the interaction between matter and electromagnetic fields. In Chapter 2, the generalized Hartree-Fock formalism with variational magnetic field is outlined and applied for simulating the non-collinear spin in molecular systems induced by external magnetic field. We show that the two component formalism is a natural choice for accommodating the spin collinearity in strong magnetic field. Chapters 3 and 4 present a new simulation method for magnetic circular dichroism based on linear response with variational treatment of magnetic fields. This variational treatment is advantageous in both calculation efficiency and the ability of approaching strong magnetic field compared with the traditional perturbation theory. We also include spin-orbit coupling variationally, which enables the simulation of temperature dependence of MCD for open-shell systems. The non-collinear density functional theory (DFT) and time-dependent density funcrional theory (TDDFT) are implemented with finite field gauge including atomic orbital (GIAO) to mitigate the gauge origin dependence problem in simulating magnetic properties. In Chapter 5, the MCD simulation method by real time electronic dynamics with variational treatment of magnetic fields is outlined. We showed the relationship between the MCD signal and the magnetically perturbed electric dipole-dipole response function.