Chemical transferability of single- and multiple-scattering EXAFS Debye-Waller factors

Single- and multiple-scattering EXAFS Debye-Waller factors are amplitude re duction parameters that appear in the EXAFS chi (k) equation accounting for the structural and thermal disorder of a given sample. These parameters mu st be known accurately in order to obtain quantitative agreement between th eory and experiment. Since experimental data can only support a limited num ber of fitted parameters these factors must be known from another source. A lthough various approaches have been considered in the past with a variety of results, the self-consistent ab initio Density functional theory stands for the most accurate and reliable method regardless of molecular symmetry or other specific sample requirements. Since DFT scales as N-3 where N is t he number of atomic basis set, an ab initio calculation on a large structur e is not feasible due to enormous CPU demand and in many cases due to hard energy/geometry convergence. In this paper we present two ways of overcomin g this problem. Both they use the idea that by reducing the structure, the DWFs are still chemically transferable. In order to test this we use the Zn tetraimidazole. This molecule represents typical metalorganic ring samples that can be seen in active sites of metaloproteins. Results are compared t o experimental EXAFS spectra.