An improved method for efficient computation of paramagnetic57Fe(III) Mossbauer relaxation spectra

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Abstract
The supermatrix Liouville formalism for the computation of Mossbauer relaxation spectra, if applied to the 6S5/2 state of 57Fe(III), leads to a 288-dimensional non-Hermitian matrix. Diagonalisation and inversion of this matrix requires far too much computer time to be used within least-squares fitting routines. Provided that an axial crystal field of sufficient strength acts on the electronic states of Fe(III), only a few of the states described by the supermatrix are necessary to simulate Mossbauer spectra. Thus the dimension of this matrix can be reduced to at least a third. Such confinement to a fraction of the original supermatrix involves no approximation for either the description of the six electronic states of Fe(III) or their time-independent interactions with surroundings and nucleus. In addition, no restrictions beyond those common to previous computations are imposed on the description of those interactions which define the relaxation matrix. The authors present a detailed description of two methods to calculate Fe(III) Mossbauer relaxation spectra; both allow not only the comprehensive simulation of theoretical Fe(III) relaxation spectra but also, for the first time, the application of least-squares procedures to interpret experimental spectra reliably.