Ma Xiao-Guang

LOVO Electrons: The Special Electrons of Molecules in Positron Annihilation Process

The electrons in the lowest occupied valence orbital (LOVO) of molecules have been found to dominate the gamma-ray spectra in the positron–electron annihilation process. The mechanism of this phenomenon is revealed in the present work for the first time. Theoretical quantitative analyses are applied to all noble gas atoms and molecules CH4, O2, C6H6, and C6H14. More than 70% of LOVO electrons and less than 30% of highest occupied molecular orbital (HOMO) electrons distribute within the full width at half-maximum (FWHM) region of the momentum spectra averagely. This indicates that the LOVO electrons have at least 2 times of probabilities than the HOMO electrons within this area. The predicted positron annihilation spectra are then generally dominated by the innermost LOVO electrons instead of the outmost HOMO electrons under the plane-wave approximation.

Theoretical studies on the photoionization cross-sections of solid silver

An alternative expression for photoionization cross-section of atoms or molecules and a dielectric influence function (DIF) in a high-density system proposed recently are used to study the photoionization cross-sections of solid silver. It is suggested that a density turning point (DTP) of a photoionized system may be viewed as the critical point where the photoionization properties of atoms in a real system may have a notable change. The results show that the present theoretical photoionization cross-sections are in good agreement with the experimental results of a silver crystal both in structure and in magnitude.

Theoretical Studies on Expressions of Condensed-Phase Photoionization Cross Section

A set of general expressions for photoionization cross sections of atoms or molecules embedded in a medium and a dielectric influence function are derived based on Maxwells equations and the Beer–Lamberts law in this work. The applications are performed for the photoionization process of solid gold both in the Clausius–Mossotti (virtual cavity) model and the Glauber–Lewenstein (real cavity) model firstly. The results show that the present theoretical expressions of photoionization cross section can be used to describe the photoionization process of atoms in condensed matter properly.

Potential energy curve study on the 3Π electronic states of GaX (X = F, Cl, and Br) molecules

The potential energy curves (PECs) of the 3Π states of GaX (X = F, Cl, and Br) molecules are calculated using the multireference configuration interaction method with a large contracted basis set aug-cc-pV5Z. The PECs are accurately fitted to analytical potential energy functions (APEFs) using the Murrell—Sorbie potential function. The spectroscopic parameters for the states are determined using the obtained APEFs, and compared with the theoretical and experimental data available presently in the literature.

A full-dimensional analytical potential energy surface for the F+CH4→HF + CH3 reaction

A full-dimensional analytical potential energy surface (APES) for the F + CH4 →HF + CH3 reaction is developed based on 7127 ab initio energy points at the unrestricted coupled-cluster with single, double, and perturbative triple excitations. The correlation-consistent polarized triple-split valence basis set is used. The APES is represented with a many-body expansion containing 239 parameters determined by the least square fitting method. The two-body terms of the APES are fitted by potential energy curves with multi-reference configuration interaction, which can describe the diatomic molecules (CH, H2, HF, and CF) accurately. It is found that the APES can reproduce the geometry and vibrational frequencies of the saddle point better than those available in the literature. The rate constants based on the present APES support the experimental results of Moore et al. [Int. J. Chem. Kin. 26, 813 (1994)]. The analytical first-order derivation of energy is also provided, making the present APES convenient and efficient for investigating the title reaction with quasiclassical trajectory calculations.

Influence of Integral Instability of Kramers–Kronig Transformation on Photoabsorption Cross Sections

The photoabsorption cross sections of condensed atoms and molecules have proven to be dependent not only on the imaginary parts but also on the real parts of the polarizabilities due to the strong interatomic interactions in condensed environment. The real parts of the polarizabilities calculated usually by using the famous Kramers–Kronig transformation (KKT) from the photoabsorption cross sections of the isolated atoms are very sensitive to the accuracy of the implementation method of the infinite integral in the KKT. The influence of the integral instability of the KKT and the real part of the polarizability on the variation of the photoabsorption cross sections with the number density and the structure of the condensed matter has been studied in the present work for the first time. The conclusion is that the integration method with interpolation has given more reasonable results than the direct truncation method if some appropriate interpolation functions have been used. Some notes and conclusions have also been given for the applications of the alternative coupled expressions of photoabsorption cross sections.

An alternative view of condensed-phase photoionization

This paper proposes an accurate valuable interpretation scheme to study the evolvement of the photoionization processes from the isolated to the condensed atoms by a unique ab initio method. The variations of the photoionization cross sections of the atomic sodium with the photoelectron energy and the boundary radius of the atomic configuration space are studied in this new scheme by the R-matrix method. The discrepancy in the photoionization spectra of the isolated and the condensed sodium has been explained quantitatively and understood successfully by this alternative view in detail for the first time.

Application of the second-order ground-state correlation and random-phase approximation on photoionization cross section of manganese

Using the many-body perturbation theory, we have calculated the photoionization cross section of 3p and 3d subshells of the neutral manganese and discussed the second-order ground-state correlation and random-phase approximation correlations in detail. This is the first theoretical calculation for manganese as far as we know. Our calculated results are more consistent with the experimental results than those given by other methods in the literature.