Home – Home – Jornals – Advanced Search

Total, difference, and deformation electron densities are calculated from the first principles using the density functional theory and the sublattice method for LiBX (B = Mg, Ca, Zn; X = N, P, As) crystals with the sphalerite structure. The nature and formation features of the chemical bonding caused by a change in the chemical composition are revealed. A weak bond between Li⁺ ions with X anions enables their displacements in the space between crystal-forming tetrahedral (BX)^- groups. It is found that Ca-X bonds are mainly ionic and in a series of crystals the ionic covalent Li-B bond is traced.

DFT and HF methods implemented in the PC GAMESS-Firefly program package are employed to calculate the spatial and electronic structures of molecules of three-coordinate aluminum compounds with Al-N bonds. NBO and AIM methods are applied to determine the main characteristics of Al-N and N-С bonds in these molecules. It is shown that Al and N atoms interact with each other as closed shell atoms. The N-С bonds are close to covalent ones.

Using first-principles pseudo-potential plane wave method, the formation enthalpy D H , binding energy D E , elastic constants, and electronic structure were calculated and analyzed carefully for NiTiX (X = Cu, Fe) shape memory alloy. The results show that the Cu or Fe element prefers to occupy the Ni site in the NiTi matrix phase respectively. Compared with the NiTi matrix phase, the D H , D E , c ₄₄ and c ¢ of NiTi (Cu) are similar to each other. However, the structural stability of the NiTi phase is improved obviously by the Fe alloying process. Simultaneously, the shear modulus c ₄₄ and c ¢ of NiTi (Fe) are larger than those of the NiTi matrix phase. Furthermore, Milliken population results indicate that Q _Cu-Ti is smaller than Q _Ni-Ti after the Cu alloying process, but Q _Fe-Ti is larger than Q _Ni-Ti. The electron density difference shows that some covalent bonding exists between Fe and Ti elements. Based on the upward analysis, the difference in the phase stability and elastic constants of NiTiX (X = Cu, Fe) is the substantial mechanism for the different M _s of NiTiX (X = Cu, Fe) although Cu or Fe substitutes for the same atom Ni elements in the NiTi matrix phase.

A quantum chemical simulation of the structure of a hydrated phenylalanine zwitterion, dimers and larger phenylalanine associates in an aqueous solution is performed by the hybrid B3LYP density functional method with the 6-31G++( d , p ) basis set. It is shown that the association of the amino acid occurs by the formation of hydrogen bonds between phenylalanine amino carboxyl groups involving water molecules.

³¹P, ¹⁹F, ¹H NMR is used to study fluorophosphatometalates of the composition MHfF₂PO₄×0.5H₂O (M = Rb, Cs) and CsMe₂F₆PO₄×4H₂O (Me = Zr, Hf). The data obtained indicate the isostructurality of compounds in each of these two groups. The lines in the NMR spectra are assigned. Assumptions about the character of the bond of PO₄ groups and F atoms with Me are made and schemes of the crystal structure of fluorophosphatometalates are proposed. The occurrence of several types of crystallization water characterized by different bond strengths and energy barriers of the diffusion motion is found.

By electron paramagnetic resonance spectroscopy the paramagnetic centers are investigated in SiC _x N _y H _z films obtained by plasma-enhanced chemical deposition from hexamethyldisilazane vapor. It is found that the films contain dangling bonds broken at carbon atoms, their concentration considerably increasing with an increase in the deposition temperature. By Raman spectroscopy a deposition temperature range is determined within which the films contain carbon clusters. Similarity in the properties of the films synthesized at high deposition temperatures and the films initially deposited at low temperatures and then annealed is established. The results of the study are interpreted with the use of the known data on the film composition and structure and also the representations described in the literature.

The efficiency of the application of the transmission X-ray diffraction technique implemented with the use of the VEPP-3 synchrotron radiation source to obtain functions of the radial electron density distribution (REDD) is shown. By the example of a poorly crystallized sample of cerium oxalate the possibilities of the obtained REDD functions in the structural diagnostics of X-ray amorphous materials are demonstrated: the oxalate phase is detected, the features of the local structure are revealed, and the size of the atomic ordering region is determined.

The carbon K -edge NEXAFS spectra of initial and fluorinated and hydrogenated single-wall carbon nanotubes (SWCNTs) are analyzed theoretically with regard to the polarization dependence. Differences in the polarized theoretical spectra of SWCNTs with zigzag and chair chiralities are shown. As a result of the comparison of experimental and theoretical carbon K -edge NEXAFS spectra of hydrogenated and fluorinated SWCNTs it is found that it is most probable that hydrogen atoms attach to the outer surface of the tube wall and fluorine atoms to the outer and inner surfaces of the SWCNT wall. Based on the analysis of polarized theoretical spectra of fluorinated and hydrogenated SWCNTs differences in the symmetry of the final states of С-H and С-F bonds are shown.

An express analysis technique for the determination of the structural properties of water clusters with impurities and the number of contained water molecules more than 12 is developed. The technique is based on the derivation of three matrices for a water cluster, which makes it possible to write down the unique code characterizing its structure. The technique significantly decreases the computation time (approximately 10⁴ times) in comparison with the procedure developed previously [1], and consequently, allows the analysis of the structural properties of aqueous systems with a large number of molecules on usual PCs. In order to illustrate the technique the code for the typical configuration of the (H₂O)₁₃ cluster is determined within the water model at a temperature of 268 K and a density of 0.99930 g/cm³.

A study is made of the temperature and concentration dependences for conductance of aqueous sodium decyl sulfate solutions. The nature of hydration of the decyl sulfate anion is discussed within the theories proposed by Samoilov, Gurikov, and Krestov. An analysis is performed of the influence of the hydration type on the critical micelle concentration. The analysis suggests that an increase in temperature stimulates micelle formation given that hydration is negative.