Liquid-state paramagnetic relaxation from first principles

Abstract

We simulate nuclear and electron spin relaxation rates in a paramagnetic system from first principles. Sampling a molecular dynamics trajectory with quantum-chemical calculations produces a time series of the instantaneous parameters of the relevant spin Hamiltonian. The Hamiltonians are, in turn, used to numerically solve the Liouville--von Neumann equation for the time evolution of the spin density matrix. We demonstrate the approach by studying the aqueous solution of the ${\mathrm{Ni}}^{2+}$ ion. Taking advantage of Kubo's theory, the spin-lattice $({T}_{1})$ and spin-spin $({T}_{2})$ relaxation rates are extracted from the simulations of the time dependence of the longitudinal and transverse magnetization, respectively. Good agreement with the available experimental data is obtained by the method.