Abstract:
The potential energy curves of the lowest 20 electronic states in the representation ^{2s+1}Λ^{(±) }of the molecule PbO have been investigated via ab initio CASSCF and MRCI (single and double excitations with Davidson correction) calculations. The spectroscopic constants such as vibrational harmonic frequency ω_{e}, the internuclear distance at equilibrium R_{e}, the rotational constant B_{e}, and the electronic transition energy T_{e} with respect to the ground state have been calculated along with the permanent dipole moment for the different bound investigated electronic states. By using the canonical functions approach, the eigenvalues E_{v}, the rotational constant B_{v} and the abscissas of the turning points R_{min} and R_{max} have been calculated. The comparison of these values with those available in the literature shows a very good agreement.

Abstract:
In this work, we have investigated the electronic and optical properties
of the technologically important rare earth oxide compounds—X_{2}O_{3} (X: Gd, Tb) using the density functional theory within the GGA. The band
structure of X_{2}O_{3} have been calculated along high
symmetry directions in the first brillouin zone. The real and imaginary parts
of dilectric functions and the other optical responses such as energy-loss
function, the effective number of valence electrons and the effective optical
dielectric constants of the rare earth sesquioxides (Gd_{2}O_{3} and Tb_{2}O_{3}) were calculated.

Abstract:
The Complete Active Space Self Consistent Field (CASSCF) with Multi Reference Configuration Interaction (single and double excitation with Davidson correction) MRCI + Q method has been used to investigate the potential energy curves of the 17 low-lying triplet electronic states of the molecule BP. The harmonic vibrational frequency ω_{e}, the inter-nuclear distance at equilibrium Re, the rotational constant B_{e}, the electronic energy with respect to the minimum ground state energy T_{e}, and the permanent dipole moment have been also calculated. A literature review shows a strong correlation between our investigated data and those previously published either theoretically or experimentally. This work introduces, for the first time, a study of 14 new electronic states. Our spectroscopic data can be a conducive to further work on BP molecule in both experimental and theoretical research.

Abstract:
Adiabatic potential energy curves of 12 doublet and quartet lowest spinless electronic states of the molecule CsO have been investigated via ab initio CASSCF and MRCI (doublet and quartet excitations with Davidson correction) calculations. The spectroscopic constants such as vibrational harmonic frequency ω_{e}, the internuclear distance at equilibrium R_{e}, the rotational constant B_{e}, and the electronic transition energy T_{e} of the ground and the excited electronic states have been calculated by fitting the energy values around the equilibrium position to a polynomial in terms of the internuclear distance. The comparison of these values to those available in the literature shows a good agreement.

Abstract:
The theoretical investigation of the potential energy curves, in the representation ^{2s+1}Λ^{(+/-)}, of the 27 low-lying Doublet and Quartet electronic states of the BP+ molecular ion has been performed with the methods in quantum chemistry, the Complete Active Space Self Consistent Field (CASSCF) and the Multireference Configuration Interaction (MRCI) calculations. The harmonic vibrational frequency ω_{e}, the inter-nuclear distance at equilibrium R_{e}, the rotational constant B_{e}, the electronic energy with respect to the minimum ground state energy T_{e}, and the permanent dipole moment have also been calculated. Twenty-three new electronic states have been investigated here for the first time. The comparison between the values of the present work and those available in the literature for several electronic states shows a good agreement. These investigated data can be a conducive to further work on BP^{+} molecular ion in both experimental and theoretical research.

Abstract:
Theoretical investigation of the lowest electronic states of ScSe molecule, in the representation ^{2s+1}Λ^{(+/-)}, has been performed via CASSCF and MRCI + Q (single and double excitations with Davidson correction) calculations. The calculated potential energy curves (PECs), permanent dipole moment curves (PDMCs), and spectroscopic constants are reported for the 14 lowest electronic states. The comparison of the present results with the rare available theoretical data in literature shows an overall good agreement. To the best of our knowledge, 13 electronic states of the ScSe molecule are not yet investigated either experimentally or theoretically; they are investigated in the present work for the first time.

Abstract:
The potential energy curves (PECs) of the16 lowest electronic states in the representation ^{2s+1}Λ^{ (+/-)} of the molecule ScTe have been investigated via ab initio CASSCF and MRCI (single and double excitations with Davidson correction) calculations. The permanent dipole moment curves (PDMCs) and the spectroscopic constants such as vibrational harmonic frequency ω_{e}, the internuclear distance at equilibrium R_{e}, the rotational constant B_{e}, and the electronic transition energy T_{e} with respect to the ground state have been calculated for the different bound investigated electronic states. The comparison of the present results with the rare available theoretical data in literature shows an overall good agreement. To the best of our knowledge, 15 electronic states of the ScTe molecule are not yet investigated either experimentally or theoretically, they are investigated in the present work for the first time.

Abstract:
Complete Active
Space Self Consistent Field (CASSCF) with Multireference Configuration Interaction
(MRCI) and Rayleigh-Schrodinger Perturbation Theory (RSPT2-RS2) methods have been
used to investigate the potential energy curves for the 12 low-lying singlet and
triplet electronic states in the representation ^{2s+1}Λ^{(+/-) }of
the molecule BaS with Davidson corrections. The harmonic frequency w_{e}, the internuclear
distance R_{e}, the electronic energy with respect to the ground state T_{e},
the rotational constants B_{e} and the permanent dipole moment have been
calculated for these electronic states. The eigenvalues E_{v}, the rotational
constants B_{v}, the centrifugal distortion constant D_{v} and the
abscissas of the turning points R_{min} and R_{max} have been investigated
using the canonical functions approach. Nine new electronic states have been investigated
here for the first time. The comparison between the values of the present work and
those available in the literature for several electronic states shows a good agreement.

Abstract:
Theoretical investigation of the lowest electronic states of ScS
molecule, in the representation ^{2s+1}Λ^{(+/-)}, has been
performed via CASSCF and MRCI (single and double excitations without Davidson
correction) calculations. The calculated potential energy curves (PECs),
permanent dipole moment curves (PDMCs), and spectroscopic constants are
reported for the 10 lowest electronic states. The eigenvalues E_{v},
the rotational constants B_{v}, and the centrifugal distortion
constants D_{v} have been calculated for various vibrational levels.
The comparison of the present results with the available experimental data in
literature shows an overall good agreement. To the best of our knowledge, 6
electronic states of the ScS molecule, between 11600 cm^{-1} and 15000
cm^{-1} are not yet observed experimentally and are investigated in the
present work for the first time.

Using ab initio density functional theory calculations, the electron localization function (ELF) of typical transition metal carbide TiC and nitride TiN were computed and analyzed to reveal their nature of the chemical bonds. The ELF approach was initially validated through typical examples of covalent-bonding Diamond (C) and ionic-bonding sodium chloride NaCl. Our results clearly demonstrate the dominantly ionic bonding characteristics of TiC and TiN. It is also suggested that the high mechanical hardness of TiC and TiN can be explained without evoking strong covalence.