Spin-Hamiltonian Parameters from First Principle Calculations: Theory and Application

Abstract

EPR spectroscopists have refined the art of interpreting experimental results by means of an effective spin-Hamiltonian (SH) to a high degree of sophistication [1]. The SH parameters are the principal outcome of an EPR experiment and represent a concise summary of the information content of the experiments. However, the power of the SH approach extends far beyond summarizing experimental results. The SH describes the physics of spin systems so well that it can be used to creatively design new experiments. The behavior of the spin system can be simulated in advance through exact solutions of the quantum mechanical equations of motions in the SH formalism. In this respect it is of major utility that the SH is so simple—it usually works in a low-dimensional Hilbert space that is only spanned by the (effective) spin degrees of freedom of the system under investigation [2]. Due to this simplicity, exact solutions are relatively easy to generate with ordinary computational hardware, or, in many cases, just with paper and pencil.