Calculations of magnetic properties. V. Electron-correlated hypermagnetizabilities (Cotton–Mouton effect) for H2, N2, HF, and CO

Abstract
Calculations of the hypermagnetizabilities (η) at the self-consistent-field (SCF) and second-order Mo/ller–Plesset perturbation theory (MP2) levels of theory are reported for H2, N2, HF, and CO. Electron correlation is found to be unimportant for H2, but very important for the other three molecules. The individual components of η are more affected by correlation effects than the hypermagnetizability anisotropy (Δη) which mediates the birefringence of a material in the presence of a magnetic field (the Cotton–Mouton effect). The zero-point-vibrational averaging, pure vibrational corrections, and frequency dependence are important for the individual components, but are less important for Δη due to cancellation between the various contributions. Excellent agreement is found with the previous theoretical results for H2, but only fair agreement with the experimental results for N2 and CO.