Electric Quadrupole and Hexadecapole Moment, Dipole and Quadrupole Polarizability, Second Electric Dipole Hyperpolarizability for P2, and a Comparative Study of Molecular Polarization in N2, P2, and As2

Abstract

We have obtained electric properties of P⋮P from finite-field Møller−Plesset perturbation theory, density functional theory and coupled cluster techniques. Reference, near-Hartree−Fock values have been obtained with a very large (20s15p10d5f) uncontracted basis set consisting of 300 Gaussian-type functions. At the experimental equilibrium bond length of Re = 1.8934 Å we obtain self-consistent field values of 1.0682 ea02 for the quadrupole moment (ϑ), −41.68 ea04 for the hexadecapole moment (Φ), 51.16 for the mean ( ) and 28.58 e2a02Eh-1 for the anisotropy of the dipole polarizability, and 16.5 × 103 e4a04Eh-3 for the mean second dipole hyperpolarizability ( ). Electron correlation reduces strongly the magnitude of the electric moments. Both components of the dipole polarizability are reduced by electron correlation, but a small increase is observed for the dipole hyperpolarizability. Our best post-Hartree−Fock values have been obtained with a [9s7p5d3f] basis set at the CCSD(T) level of theory: ϑ = 0.4850 ea02, Φ = −31.25 ea04, = 49.20 and Δα = 28.02 e2a02Eh-1, = 16.8 × 103 e4a04Eh-3. The bond-length dependence around Re has been obtained for all properties. Conventional density functional theory methods predict dipole polarizabilities close enough to the most accurate CCSD(T) values but overestimate the second dipole hyperpolarizability. The mean dipole polarizability changes as (NaK) > (AlCl) > (SiS) > (P2) > (Zn) for some isoelectronic, 30-electron systems. It is seen that the electric properties in the sequence N2→P2→As2 display regular changes.