Abstract
We investigate the availability of Debye and Einstein approximations to calculate Debye-Waller factors in EXAFS, EELS and ARXPS for one-dimensional models. These approximate results were compared with the ab initio results shown in the previous paper II. For monatomic chains the Debye model can give a good result even for third and fourth cumulants. In the case of diatomic chains, a mixed model where Debye (Einstein) approximation is used for acoustic (optical) mode give quite a good result for harmonic second order cumulant. This simple approximation, however, gives rather poor results for third and fourth order cumulants and also anharmonic correction to the second order cumulant. This result is due to the fact the phases of the eigenvectors of the dynamical matrix play an important role for the accurate estimation of those thermal factors.
