MAGNETIC GROUND-STATE PROPERTIES AND SPECTRAL DISTRIBUTIONS .1. X-RAY-ABSORPTION SPECTRA

We develop the method of statistical moments for polarized spectra. In addition to the total intensity measured by sum rules, the average transition energy can be studied. A general procedure is given to remove core-level excitations from the spectrum operator and to obtain purely ground-state properties. The potential of the methods is shown by a rederivation of the x-ray-absorption sum rules and branching-ratio rules for the isotropic spectrum and linear and circular dichroism. Insight is obtained into the origins of changes in the first moment of the isotropic spectrum. They measure short-range correlation functions of crystal and exchange fields. © 1994 The American Physical Society.