Concept of effective states of atoms in compounds to describe properties determined by the densities of valence electrons in atomic cores

Abstract

We propose an approach for describing the effective electronic states of "atoms in compounds" to study the properties of molecules and condensed matter which are circumscribed by the operators heavily concentrated in atomic cores. Among the properties are hyperfine structure, space parity (P) and time reversal invariance (T) nonconservation effects, chemical shifts of x-ray emission lines (XES), Mössbauer effect, etc. An advantage of the approach is that a good quantitative agreement of predicted and experimental data can be attained even for such difficult cases as XES chemical shifts providing correct quantum-mechanical interpretation of the experimental data. From the computational point of view the method can be quite efficient being implemented in the framework of the relativistic pseudopotential theory [A. V. Titov and N. S. Mosyagin Int.J. Quantum Chem. 71, 359 (1999)] and procedures of recovering the wave functions in heavy-atom cores [A. V. Titov, N. S. Mosyagin, A. N. Petrov, and T. A. Isaev, ibid. 104, 223 (2005)] after a molecular, cluster or periodic structure calculation performed on the basis of pseudoorbitals smoothed near the nuclei within the pseudopotential approximation. We report results of our studies of a number of atomic and molecular systems to demonstrate the capabilities of the approach.

TaN molecule as a candidate for the search for aT,P-violating nuclear magnetic quadrupole moment

“…After this stage we obtain wavefunction that is very accurate in the valence region but has incorrect behaviour in the core region. The correct four-component behaviour of the wave-function in the core region is restored at the second step using the procedure [32,52] based on a proportionality of valence and virtual (unoccupied in the reference Slater determinant) spinors [64] in the inner-core regions of heavy atom. The splitting of solution of the four-component relativistic full-electron problem on two consequent steps allows one to consider high-order correlation effects (see below) that are important for reliable and accurate calculation of the properties that cannot be measured experimentally.…”

CHEMICAL SHIFTS OF X-RAY EMISSION SPECTRA AND EFFECTIVE STATES OF YTTERBIUM IN FLUORIDES: EMBEDDED CLUSTER MODELING OF YbF2 AND YbF3 CRYSTALS

“…The theoretical investigation of such systems should take into account both the relativistic and correlation effects very accurately. In references [4] and [5], a method of evaluating chemical shifts of X-ray emission lines is described, which is applicable to such kind of systems. It is based on the relativistic pseudopotential model and one-center restoration approach [6] to recover a proper electronic structure in heavy-atom cores after the pseudopotential simulation of chemical compounds.…”

“…Such a change of the electronic density in the spatial outercore region (where 4f shell is localized) results in a large chemical shift (ChSh) of the characteristic X-ray emission lines (XES) on Yb. Therefore, the determination of the XES chemical shifts can be an efficient tool for studying changes in the valence states of d and f elements in a chemical compound [1]- [5].…”

Расчет Химических Сдвигов Рентгеновских Эмиссионных Спектров Ниобия В Оксидах Ниобия(V) Относительно Металла-=sup=-*-=/Sup=-

“…По изменению положения спектральной линии харак-теристического излучения атома в различных соеди-нениях (химическом сдвиге линии) можно судить о его cостоянии окисления и других свойствах. В рабо-тах [4,5] предложен метод расчета химических сдвигов рентгеновских эмиссионных линий на основе результа-тов квантово-механического моделирования соединений. В работе [6] был проведен расчет химических сдвигов ниобия в ферсмите (CaNb 2 O 6 ) относительно металла и проведено сравнение с экспериментальными данными (величина химического сдвига K α1 -линии ниобия в этом соединении около 260 meV, теоретическое значение -около 300 meV).…”

“…Расчет химических сдвигов линий K α1 и K β1 ниобия в этих кластерах позволяет детально проанализировать точность предложенного метода [4,5], а также изучить влияние размера рассматриваемых кластеров на величи-ну химического сдвига.…”