Finite-field Møller–Plesset perturbation theory and coupled cluster calculations of the electric multipole moments and the dipole polarizability of As2 Original Research Article

We have calculated the quadrupole (Θ) and hexadecapole (Φ) moment and the static dipole polarizability (ααβ) of As2. The electric properties have been extracted from finite-field Møller–Plesset and coupled cluster calculations with large, carefully optimized basis sets of Gaussian-type functions. A very large (21s16p10d4f) basis set is thought to provide near-Hartree–Fock values for the electric moments, the mean and the anisotropy of the dipole polarizability: Θ=1.46ea02, Φ=−52.4ea04, α=64.95 and Δα=40.37e2a02Eh−1. At the SDQ-MP4 level of theory the R-dependence of the electric properties has been calculated with a [7s6p5d2f] basis set as[Θ(R)−Θ(Re)]/ea02=2.84(R−Re)−0.87(R−Re)2−0.32(R−Re)3−0.21(R−Re)4[Φ(R)−Φ(Re)]/ea04=21.0(R−Re)+8.7(R−Re)2−1.6(R−Re)3−2.0(R−Re)4[α(R)−α(Re)]/e2a02Eh−1=17.42(R−Re)−0.048(R−Re)2−0.33(R−Re)3+1.71(R−Re)4[Δα(R)−Δα(Re)]/e2a02Eh−1=22.62(R−Re)+6.68(R−Re)2+2.79(R−Re)3+1.04(R−Re)4around the experimental bond length of Re=2.1026 Å. Basis set effects have been studied at all levels of theory. Comparing the electric properties of the sequence N2, P2, As2 it is seen that the quadrupole moment is negative for N2 but positive for P2 and As2 while the hexadecapole is negative for all three diatomics. The mean dipole polarizability increases with size, α(N2)<α(P2)<α(As2) and the same trend is observed for the anisotropy as well, Δα(N2)<Δα(P2)<Δα(As2).