Molecules in static electric fields: Linear and nonlinear polarizability of HC≡N and HC≡P
Résumé
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=8.38e2a20E-1 H. For HCP the respective values are 35.47 and 16.24 e2a20E-1H. Electron correlation reduces significantly the magnitude of the first dipole hyperpolarizability (βαβγ) 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) e3a30E-2H for HCP. Electron correlation modifies mainly the longitudinal component of the second hyperpolarizability tensor γαβγδ for both HCN and HCP. The CCSD(T) mean value for HCN is γ̄=22.0×102, 17.4% higher than the SCF value of 18.8×102e4a40E -3H. For HCP γ̄=10.2×103 at the CCSD(T) level, only 2.2% above the SCF result of 99.8×102e4a40E -3H. For the quadrupole polarizability, fourth-order many-body perturbation theory yields Czz,zz=68.58, Cxz,xz=40.51, Cxx,xx=34.98 e2a40E-1H for HCN, and Czz,zz=202.28, Cxz,xz=114.44, Cxx,xx=106.38 e2a40E-1H for HCP, with z as the molecular axis.