Molecules in static electric fields: Linear and nonlinear polarizability of HC≡N and HC≡P

Abstract

Accurate linear and nonlinear polarizabilities were obtained from finite-field self-consistent field, fourth-order many-body perturbation theory and coupled-cluster calculations for the triply bonded linear molecules H-G≡N and H-C≡P. The mean dipole polarizability and the anisotropy of HCN at the CCSD(T) level of theory is ᾱ=16.74 and Δα=8.38e 2 a 2 0 E -1 H . For HCP the respective values are 35.47 and 16.24 e 2 a 2 0 E -1 H . Electron correlation reduces significantly the magnitude of the first dipole hyperpolarizability (β αβγ ) of both molecules. The CCSD(T) values of the mean β̄ are [self-consistent-field (SCF) values in parentheses] -2.8 (-7.6) for HCN and 28.5 (36.7) e 3 a 3 0 E -2 H for HCP. Electron correlation modifies mainly the longitudinal component of the second hyperpolarizability tensor γ αβγδ for both HCN and HCP. The CCSD(T) mean value for HCN is γ̄=22.0×10 2 , 17.4% higher than the SCF value of 18.8×10 2 e 4 a 4 0 E -3 H . For HCP γ̄=10.2×10 3 at the CCSD(T) level, only 2.2% above the SCF result of 99.8×10 2 e 4 a 4 0 E -3 H . For the quadrupole polarizability, fourth-order many-body perturbation theory yields C zz,zz =68.58, C xz,xz =40.51, C xx,xx =34.98 e 2 a 4 0 E -1 H for HCN, and C zz,zz =202.28, C xz,xz =114.44, C xx,xx =106.38 e 2 a 4 0 E -1 H for HCP, with z as the molecular axis.