Multipole moments, polarizabilities, and hyperpolarizabilities for N2 from fourth-order many-body perturbation theory calculations

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Abstract
All multipole moment, polarizability, and hyperpolarizability tensors up to the fourth rank are calculated for the ground 1Σ+g state of N2 at its equilibrium bond length. These properties are obtained from fourth‐order Mo/ller–Plesset perturbation theory energies of N2 in the presence of various configurations of point charges. Electron correlation was found to affect the longitudinal components the most. Some of the anisotropies of these tensors change by as much as 105% upon inclusion of electron correlation. The results are in good agreement with all previous reliable theoretical and experimental values. The calculated values of the quadrupole–quadrupole (C) and dipole–octopole polarizabilities, and the dipole–dipole–quadrupole (B) and dipole–dipole–dipole–dipole (γ) hyperpolarizabilities are the most accurate ones available. Our best vibrationless estimates of the isotropic averages of these quantities are C̄=40.371 e2 a40 E−1h, B̄=−149 e3 a40 E−2h, and γ̄=830e4 a40 E−3h.