Modern development of x-ray technology allows to conduct a detailed study of multiphoton processes of absorption and scattering of x-ray photon by deep and subvalent shells of molecular systems in a wide range of energies. The specifics of solving the problem of interaction of an x-ray photon with a multiatomic system requires the use of a single-center approach to the calculation of the electronic States of molecules. The main disadvantage of this approach is a decrease in the accuracy of the calculation of spectroscopic quantities with limited consideration of the terms of the single-center decomposition of the molecular orbital. The paper studies the effect of accounting for higher harmonics of single-center molecular orbital decomposition on the calculation of the energy characteristics of molecular systems. The analysis of the parameters of the single-center decomposition of the functions of the nuclear ligand, depending on its charge. The criteria for inclusion of higher harmonics of single-center decomposition of atomic ligand functions in the molecular orbital are determined. The calculation of energy characteristics is performed on the example of diatomic molecules HF, LiF and BF. The selected series of molecules makes it possible to study the behavior of higher harmonics of the single-center decomposition of the molecular orbital depending on the growth of the atomic ligand charge.

Keywords: molecular orbital, single-center decomposition, higher harmonics, a nuclear ligand, the energy of the electronic state of a diatomic molecule

Investigation of the interaction of electromagnetic radiation with molecular systems gives most of the information about their structure and properties. Interpretation of experimental data is directly determined by the knowledge of the structure of energy levels and its change in the transition of these systems to an excited state. A key task of the methods for calculating the molecular orbitals of excited states is to accurately describe the emerging vacancies of the molecular core, leading to radial relaxation of the electron density. A method is proposed for an exact description of the electron density of a molecular system near its nuclei, which provides solutions to the problem of slow convergence of molecular orbitals in a single-center representation. The implementation of the computational procedure is examined using the example of a diatomic hydrogen fluoride molecule. The energy characteristics of the ground and ionized states of the molecule are estimated

Keywords: single-center method, molecular orbital, excited state, ionized state, deep shell

The paper presents an overview of the existing calculation schemes and the technique for obtaining the angular parts of the matrix elements of the spectroscopic quantities operators with the discussion of cases of complex electron configurations containing nonequivalent electrons. Using the example of a configuration with four unfilled electronic shells, the high efficiency of the technique for constructing wave functions of arbitrary electronic configurations is shown, based on a combination of Slater's determinant approach and the procedure for sequential coupling of orbital and spin moments on the basis of the Clebsch-Gordan coefficients in the LS coupling approximation.

Keywords: Slater determinant, Clebsch-Gordan coefficient, orbital angular momentum, spin moment, 3j-symbol, coefficients of fractional parentage, LS-coupling

The paper represents the results of theoretical study of molecules behavior of polar aprotonic solvent dimethyl sulphoxide on basal surfaces and in interpackage space of kaolinite. Spectral and energetic regularities of chemical bond formation are studied. Intercalation of DMSO molecules into interpackage space of kaolinite results in the shift of valence vibrations Si-O into high-frequency zone. It also results in vibration suppression of hydroxyl clusters of gibbsite layer. It proves the appearance of strong hydrogen bond between the molecules of polar aprotonic dissolvent and hydroxyl and siloxane kaolinite surfaces. The paper reveals that adsorption of DMSO molecules decreases the surface energy of kaolinite and enables its organophilicity.

Keywords: "layered aluminosilicates dimethyl sulfoxide, density functional theory, intercalation, hydroxyl surface siloxane surface kaolinite"