Mohammadou Mérawa

Structural, electronic and elastic properties of some fluoride crystals: an ab initio study

Abstract The structural, electronic and elastic properties, as well as the IR and Raman central zone phonon frequencies of CaF 2 , SrF 2 and BaF 2 , have been evaluated by using the periodic ab initio linear combination of atomic orbitals method implemented in the CRYSTAL package. The Hartree–Fock and different density functionals, namely the local density (LDA) and the generalized gradient (GGA), as well as the hybrid B3LYP, Hamiltonians, have been used. The binding energy, equilibrium lattice parameter, elastic constants ( C ij ) and central zone phonon frequencies exhibit a regular and consistent trend in the series, in good agreement with experimental data.

Structural, electronic, and vibrational properties of solid Sr(OH)2, calculated with different Hamiltonians

The structural equilibrium parameters, the energetic of formation and hydration processes, and the O–H vibrational frequencies of crystalline Sr(OH)2 have been investigated at the ab initio level using the periodic CRYSTAL package. Both Hartree–Fock (HF) and density functional theory (DFT) Hamiltonians have been used, the latter in its local density (LV), gradient-corrected (PP), and hybrid (B3LYP) versions. The computed Sr(OH)2 structural parameters are in reasonable agreement with experiment, the largest deviation being for the a cell parameter, which is overestimated by all the adopted methods. With respect to experiment, DFT Hamiltonians give errors of the order of 13% for the formation energies, whereas errors for the heats of hydration from the corresponding oxide are as large as 27% for the LV functional. Two families of OH groups occur in the structure, in which one acts as a weak hydrogen bond donor. The fundamental ω01(OH) stretching frequency has been computed for the two OH groups, and their d...

Excited states dipole polarizabilities of calcium atom and long-range dispersion coefficients for the low-lying electronic states of Ca2 and CaMg

Abstract The frequency-dependent dipole polarizabilities are calculated for the five lowest states 41S, 51S, 41P, 43P and 53S of Ca by using a time-dependent gauge invariant method. The difference of the polarizability (α( 3 P )−α( 1 S )) of 112.9 a.u., between the excited 3P state and the 41S ground state calculated from the TDGI method is in good agreement with the two experimental measurements of 96.5±16.4 and 90.4±13.8 a.u. obtained from the Stark frequency and phase shifts, respectively, by Morinaga et al. [Phys. Rev. A 54 (1996) 21]. As a consequence of our previous work referring to the Mg atom, the length formulation of the oscillator strengths has been used. Estimations of the long-range dispersion coefficients for the first molecular state dissociations of Ca2 and CaMg are proposed. Most of the results are new, and predict a repulsive behaviour for the 1 Π g , u and 3 Σ + g , u states of the 4 1 S –4 1 P and 5 1 S –4 1 P interactions, respectively.

Dynamic polarizability and hyperpolarizability for the 14 electron molecules CO and BF

Abstract The dynamic polarizability and hyperpolarizability for the 14 electron diatomics CO and BF have been obtained from a time-dependent gauge invariant (TDGI) method. The results compare well with both experimental and theoretical calculations for CO. The frequency-dependent dipole polarizability and hyperpolarizability presented here are new for BF. In all cases the dynamic components are calculated for the dipole polarizability and electro-optic Pockels effect for the three first resonances.

Dipole polarizabilities of Na and long-range coefficients for various molecular states of Na2

Dynamic polarizabilities are calculated for Na in its 3s 2S, 3p 2P and 4s 2S states with a time-dependent gauge-invariant (TDGI) method. Coulombic long-range interactions are deduced for various states of Na2 and compared to previous calculated and experimental results.

Ab initio calculations of dipole polarizabilities of Na and K in their 32D-state and determination of long-range coefficients for S+D molecular states of Na2,K2, and NaK

Dynamic polarizabilities of Na and K in their first excited states are calculated with a time-dependent gauge-invariant (TDGI) method, using one-electron wave functions and pseudo-potentials. The values obtained for Na and K in the low-lying S and P states are compared to our previous all-electron results. Then, the dynamic polarizabilities of Na and K in their 3d 2D state are calculated in order to determine the long-range dispersion coefficients for the dissociative S+D states of Na2, K2, and NaK.

VOH center in magnesium oxide: an ab initio supercell study

Abstract The V OH trapped-electron-hole center in magnesium oxide is studied with the periodic ab initio Hartree–Fock program crystal by using the supercell scheme. The H atom that formally is substituted for a Mg atom at its lattice position migrates towards one of the neighboring O atoms, forming a strong covalent bond with it, whereas the hole localizes at the opposite O atom completely. The electronic structure of the defect is discussed in terms of electron charge and spin density maps and band structure. The isotropic and anisotropic components of the hyperfine coupling constant between the H nucleus and the unpaired electron are calculated and are in quite good agreement with ENDOR results.

Dynamic dipole polarizabilities for the ground 4 1S and the low-lying 4 1,3P and 5 1,3S excited states of Zn. Calculation of long-range coefficients of Zn2

Dynamic dipole polarizabilities for the ground 4 1S and the low-lying 4 1,3P and 5 1,3S excited states of Zn are calculated by the time-dependent gauge-invariant method and compared with other experimental and theoretical results. The wavefunctions are obtained from multi-reference configuration-interaction calculations using a two-electron relativistic pseudopotential. Core-valence polarization is accounted for by the use of a semi-empirical core-valence potential. Core-polarization effects are also considered when calculating the oscillator strengths using a modified dipole transition operator. Long-range coefficients for the molecular states of Zn2 dissociating into: 4 1S + 4 1S; 4 1S + 4 3P; 4 1S + 4 1P; 4 1S + 5 1S and 4 1S + 5 3S are presented.

Theoretical determination of electric properties and Raman intensities of HCl and HF

Abstract The dynamic polarizabilities have been calculated at different nuclear positions in order to estimate the derivatives of the polarizability and polarizability anisotropy with respect to the internuclear separation at the equilibrium geometry. Scattering cross-section and depolarization ratio presented for several values of wave length are in very good agreement with previous theoretical results and in some cases improve significantly the agreement with the experiment. Quantitative evaluations of correlation effects are also given.

Dynamic dipole polarizabilities and C6 dispersion coefficients for small clusters of beryllium Ben (n=2,3,4)

Abstract Dipole polarizabilities ( α ), first ( β ) and second ( γ ) hyperpolarizabilities are obtained for small clusters of beryllium Be n ( n =2,3,4) in a systematic study of basis set effects from CPHF calculations. In all cases, our static results are new and serve as a benchmark for future calculations. Electron correlation obtained at the MRDCI, MP4SDQ(T) and CCSD(T) levels reduces significantly the magnitude of the mean dipole polarizability of both clusters. Dynamic dipole polarizabilities calculated using TDGI method are given for a range of real ( ω =0–0.2 a.u.) and imaginary frequencies ( ω =0–4 a.u.). Corresponding isotropic and anisotropic dispersion coefficients between these clusters are also reported.