Exploring relaxation of magnetization in paramagnetic molecules
Loading...
Authors
Nakritskaia, Daria
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
Electronic Structure , Molecular Magnetism , Quantum Algorithms
Alternative Title
Abstract
Relaxation of magnetization in paramagnetic molecules consists of several distinct mechanisms that are often difficult to elucidate. The goal of this work is to explore different theoretical approaches to uncovering contributions of different mechanisms to magnetic relaxation. We demonstrated on the examples of the DyCl6(TiCp2)3 and Dy(terpyNO2)(NO3)3 complexes that changes in molecular geometries of paramagnetic molecules due to isomerization or molecular environment (gas, solution, crystal phase) can strongly affect the magnetization relaxation mechanisms. We showed that small geometric changes induced by molecular environment can affect the resonances between the spin and vibrational states, and therefore, the Orbach relaxation rate. This finding highlights the crucial shortcoming of studying magnetic relaxation of complex molecular systems using the electronic structure of a single molecule in vacuum. The molecular dynamics simulations of the Dy(terpyNO2)(NO3)3 complex in acetonitrile solution revealed a new structure with an acetonitrile molecule coordinated directly to the Dy ion, which significantly changed the crystal field symmetry and increased the magnetic anisotropy barrier. We discovered a strong correlation between the partial atomic charges on the ligands and the effective barrier of magnetization. Based on this discovery, we proposed a new design strategy for paramagnetic molecules with large effective barrier of magnetization. Our study highlighted the important role played by the mixing of M_J pseudospin states in the relaxation of magnetization in paramagnetic molecules. We implemented a very computationally efficient crystal field based approach to calculate spin-vibrational (nonadiabatic) couplings responsible for the magnetization relaxation in lanthanide complexes. Finally, we explored the possibility of simulating the magnetization dynamics in paramagnetic molecules with multiple electron spin centers on a quantum computer. We simulated the time-evolution of a three-spin state of a paramagnetic Cu(cryptate) complex using the quantum Yang-Baxter equation (QuYBE) algorithm. We also showed that we can consider response to the external magnetic field via dielectric polarization of pairs of spins and transform the resulting Hamiltonian into that for dimerized XY chain. We argued that this can allow us to extend the applications of the QuYBE algorithm to study quench dynamics and local observables.