The electronic, vibrational and rotational contributions to the dipole moment, polarizability, and first and second hyperpolarizabilities of the BH molecule

Abstract

Electronic, vibrational and rotational contributions to the dipole moment μ, polarizability α, and first and second hyperpolarizabilities, β and γ, are presented for the boron hydride molecule; static and dynamic rovibrational properties are reported for the first time. The electronic contributions are computed ab initio by finite differencing the electronic energy computed at the Hartree–Fock level of theory, and using various sophisticated correlated methods. Specifically these are Mo/ller–Plesset perturbation theory at second order, and fourth order (including single, double, triple and quadruple substitutions), and the Brueckner variant of the coupled-cluster method including triple excitations; density functional theory with the B3LYP functional is used for comparison. Vibrational (and rotational) contributions to the properties are calculated at the Hartree–Fock level of theory; for the vibrational properties, electron correlation is partially included using second order Mo/ller–Plesset theory. Basis set and electron correlation effects on both electronic and vibrational contributions are assessed and discussed. The dependence of the vibrational properties on the mechanical and electrical anharmonicity is examined, and the two methods used in its computation — a finite difference approach and a perturbation theoretic method — are compared and contrasted. A brief analysis of the frequency dependence of vibrational contributions to α(−ωσ;ω1), β(−ωσ;ω1,ω2) in the electro-optic Pockels and second harmonic generation effects, and γ(−ωσ;ω1,ω2,ω3) in the electro-optic Kerr and electric-field-induced second harmonic generation effects, is presented. The electronic results are compared with literature values believed to the best currently available; agreement is shown to be acceptable.