Finite-field Moller-Plesset perturbation theory and coupled cluster calculations of the electric multipole moments and the dipole polarizability of As-2

We have calculated the quadrupole (Theta) and hexadecapole (Phi) moment and the static dipole polarizability (ol,p) of As-2. The electric properties h ave been extracted from finite-field Moller-Plesset and coupled cluster cal culations with large, carefully optimized basis sets of Gaussian-type funct ions. A very large (21s16p10d4f) basis set is thought to provide near-Hartr ee-Fock values for the electric moments, the mean and the anisotropy of the dipole polarizability: Theta = 1.46ea(0)(2), Phi = -52.4ea(0)(4), <(<alpha >)over bar> = 64.95 and Delta alpha = 40.37e(2)a(0)(2)E(h)(-1). At the SDQ- MP4 level of theory the R-dependence of the electric properties has been ca lculated with a [7s6p5d2f] basis set as [Theta (R) -Theta (R-e)]/ea(0)(2) = 2.84(R - R-e) - 0.87(R - R-e)(2) - 0.32 (R - R-e)(3 _) 0.21(R - R-e)(4) [Phi (R) - Phi (R-e)]/ea(0)(4) = 21.0(R - R -e) + 8.7(R - R-e)(2) - 1.6(R - R-e)(3) - 2.0(R - R-e)(4) [<(<alpha>)over b ar>(R) - <(<alpha>)over bar>(R-e)]/e(2)a(0)(2)E(h)(-1) = 17.42(R - R-e) - 0 .048(R - R-e)(2) - 0.33(R - R-e)(3) + 1.71(R - R-e)(4) [Delta alpha (R) - D elta alpha (R-e)]/e(2)a(0)(2)E(h)(-1) = 22.62(R - R-e) + 6.68(R - R-e)(2) 2.79(R - R-e)(3) + 1.04(R - R-e)(4) around the experimental bond length of R-c = 2.1036 Angstrom. Basis set eff ects have been studied at all levels of theory. Comparing the electric prop erties of the sequence N-2, P-2, As-2 it is seen that the quadrupole moment is negative for N-2 but positive for P-2 and As-2 while the hexadecapole i s negative for all three diatomics. The mean dipole polarizability increase s with size, <(<alpha>)over bar>(N-2) < <(<alpha>)over bar>(P-2) < <(<alpha >)over bar>(As-2) and the same trend is observed for the anisotropy as well , Delta alpha (N-2) < Delta alpha (P-2) < Delta alpha (As-2). (C) 2001 Else vier Science B.V. All rights reserved.