Compound-tunable embedding potential method and its application to fersmite crystal

Abstract

Compound-tunable embedding potential (CTEP) method is proposed. A fragment of some chemical compound, "main cluster" in the present paper, is limited by boundary anions such that the nearest environmental atoms are cations. The CTEP method is based on constructing the embedding potential as linear combination of short-range "electron-free" spherical "tunable" pseudopotentials for cations from nearest environment of the main cluster, whereas the long-range CTEP part consists of Coulomb potentials from optimized fractional point charges centered on both environmental cations and anions.A pilot application of the CTEP method to the fersmite crystal, CaNb2O6, is performed and a remarkable agreement of the electronic density and interatomic distances within the fragment with those of the original periodic crystal calculation is attained. Characteristics of "atoms-incompounds" [1] which are of great importance for compound of f -and d-elements (Nb in fersmite) are considered on examples of chemical shifts of Kα 1,2 and K β 1,2 lines of X-ray emission spectra in niobium. A very promising potential of this approach in studying variety of properties of point defects containing f -and heavy d-elements with relativistic effects, extended basis set and broken crystal symmetry considered is discussed.

Relativistic Fock Space Coupled Cluster Method for Many-Electron Systems: Non-Perturbative Account for Connected Triple Excitations

“…The results indicate that the decisive breakthrough in the accuracy and predictive power of the electronic structure modeling of heavy-element compounds can be achieved by the proposed way. However, further developments in both the theoretical foundations and the algorithm design are clearly required to make the FS-RCCSDT models applicable to wide classes of complex heavy-atom molecules as well as to cluster models of solids [101].…”

Compound-tunable embedding potential method and its application to ytterbium fluoride crystals YbF$_2$ and YbF$_3$

“…Compound-tunable embedding potential method developed by us in [1,2] to describe electronic structure of fragments which may contain defects with f −elements is applied to crystals containing periodically arranged lanthanide atoms. The YbF 2 and YbF 3 crystals are considered such that 4f shell is excluded from both the crystal and cluster stages of generating the CTEP to make calculations with crystal code stable.…”

“…For simulation of the crystal structure, the basis set overflow arising in presence of diffuse orbitals can be significant, since relatively small atomic basis sets are used for such studies to avoid their linear dependence. In turn, they can be well corrected in cluster calculations with compound-tunable embedding potential (CTEP) [1,2]. The electronic properties of the Yb atom in YbF 2 and YbF 3 crystals are studied using the following cluster model.…”

“…Such a fragment with embedding potential is usually called the "embedded cluster" or "cluster, embedded in a crystal". This work is devoted to theoretical modeling of ytterbium di-and tri-fluorides using compound-tunable embedding potential method described in work [1,2].…”

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Compound-tunable embedding potential (CTEP) method developed in [1,2] to describe electronic structure of fragments in materials is applied to crystals containing periodically arranged lanthanide atoms, which can have open 4f shell. We consider YbF2 and YbF3 as examples such that 4f shell is excluded from both the crystal and cluster stages of generating the CTEP.

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