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

Single- and multiple-scattering EXAFS Debye-Waller factors are amplitude reduction parameters that appear in the EXAFS chi (k) equation accounting for the structural and thermal disorder of a given sample. These parameters must be known accurately in order to obtain quantitative agreement between theory and experiment. Since experimental data can only support a limited number of fitted parameters these factors must be known from another source. Although 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 the number of atomic basis set, an ab initio calculation on a large structure 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 overcoming 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 to experimental EXAFS spectra.