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

Abstract

We have calculated the quadrupole ( Θ) and hexadecapole ( Φ) moment and the static dipole polarizability ( α αβ ) of As 2. 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=1.46 ea 0 2, Φ=−52.4 ea 0 4, α=64.95 and Δα=40.37 e 2 a 0 2 E h −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(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 [ Φ(R)− Φ(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 [ α(R)− α(R e )]/e 2a 0 2E 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 [Δα(R)−Δα(R e )]/e 2a 0 2E 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 e=2.1026 Å. Basis set effects have been studied at all levels of theory. Comparing the electric properties 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 is negative for all three diatomics. The mean dipole polarizability increases with size, α( N 2)< α( P 2)< α( As 2) and the same trend is observed for the anisotropy as well, Δα(N 2)< Δα(P 2)< Δα(As 2).