Application of the embedding potential method in calculations of the electronic structure and X-ray emission spectra of crystal MgO clusters

Abstract

K and L X-ray emission spectra of Mg atoms in a MgO crystal are calculated. The wave functions and energies of the crystal needed for calculating the intensities of these spectra are obtained in calculations of crystalline clusters by the embedding potential method. In this method, a finite cluster is considered instead of an infinite crystal and the effect of the crystalline environment on the cluster is simulated by a potential that is usually called the "embedding potential." The electronic structure of clusters of different sizes and geometries in the embedding potential field is calculated by the Hartree-Fock and density functional methods. Qualitative agreement between calculated spectra and experimental data testifies that the embedding potential correctly describes the effect of the crystalline environment on the cluster.

Quantum Mechanical/Molecular Mechanical (QM/MM) Approaches

“…To perform such a strong electron localisation, one should remove the orthonormal constraint on the wave functions, which necessitates the switch from canonical Hartree-Fock (and correspondingly Kohn-Sham in DFT) equations and their orbital solutions to noncanonical orbitals, subject to Adams-Gilbert equations (Danyliv and Kantorovich, 2004;Danyliv et al, 2007). Much effort has, therefore, concentrated on the derivation of appropriate embedding schemes (Abarenkov et al, 2011;Abarenkov and Tupitsyn, 2001;Antes and Thiel, 1999;Danyliv and Kantorovich, 2004;Danyliv et al, 2007;Guo et al, 2012;He et al, 2009;Hégely et al, 2016;Huzinaga et al, 1987;Kantorovich, 1983Kantorovich, , 1988Laino et al, 2006;Manby et al, 2012;Milov et al, 2015;Seijo and Barandiarán, 1996;Shidlovskaya, 2002;Tchougréeff, 1999Tchougréeff, , 2016Wesolowski et al, 2015). In this respect, the external potential can originate from the surroundings, represented by their charge density, giving rise to the family of so-called Density-Functional…”