Parallel calculation of electron multiple scattering using Lanczos algorithms

Abstract

Real space multiple scattering calculations of the electronic density of states and x-ray spectra in solids typically scale as the cube of the system and basis set size, and hence are highly demanding computationally. For example, x-ray absorption near edge structure (XANES) calculations in solids typically require clusters of order NR atoms and s, p, and d states for convergence, with NR between about 10 2-10 3 ; for this case about 10 2 inversions of 9NR × 9NR matrices are needed, one for each energy point. We discuss here two ways to speed up these calculations: 1) message passing interface (MPI) parallel processing, and 2) fast, Lanczos multiple scattering algorithms. Together these algorithms can reduce computation times typically by two orders of magnitude. These are both implemented in a generalization of the ab initio self-consistent FEFF8 code, which thus makes XANES calculations in complex systems with of order 10 3 atoms practical. The Lanczos algorithm also yields a natural crossover between full and finite-order multiple scattering with increasing energy, thus differentiating the extended and near-edge regimes.

Synchrotron ultrafast techniques for photoactive transition metal complexes

“…Moreover, in some cases when additional information on the ES geometry is available, the μ ES (E) contribution can be isolated, especially from the XANES portion of the XAS spectrum [148,149]. Once the ES signal is extracted, several codes can be employed to perform a combined fitting of the GS and ES structures in both the XANES [77,[150][151][152][153][154][155] and EXAFS [77,156] regions.…”

Inhibition effect of underpotential deposition of metallic cations on aqueous corrosion of metals

“…It has been clarified from the comparison with RSFs of Sn standard materials (β-Sn foil, SnO and SnO 2 ) that the peaks, P A and P B , are assigned to the Sn-O and Sn-Ni interactions, respectively. The RSFs of the surface atomic structure models proposed for the Sn-UPD layer on Ni are simulated by using the program FEFF8.2 (Ankudinov et al, 1998(Ankudinov et al, , 2002 to compare wth the real RSFs in Figure 15 by curve fitting. As a result, a Sn-incorporation model is the most suitable in which Sn atoms are substituted like in a surface alloy at face-centered cubic sites in the first Ni layer and further coordinated with oxygen atoms (Seo et al, 2014a).…”

Indium induced band gap tailoring in AgGa1−xInxS2 chalcopyrite structure for visible light photocatalysis

“…12 We reported that AgGaS 2 and AgGaS 2 / CdS nanobulk composite showed excellent activity for photocatalytic hydrogen production from electrolyte containing sulfide and sulfite under visible right irradiation ͑ ജ420 nm͒. 13,14 In an effort to fabricate an efficient photocatalyst, we tried to modulate the band structure of AgGaS 2 by substitution of indium into the Ga site in the AgGaS 2 lattice. The AgGaS 2 is a p-type semiconductor with a direct band gap energy of ϳ2.68 eV.…”