The electric-field-gradient-induced birefringence and the determination of molecular quadrupole moments

A review is made of the status of computational analysis of the Electric Field Gradient induced birefringence (EFGB) in atoms and molecules. EFGB experiments are a standard means to determine molecular electric quadrupole moments, or, if coupled to measurement of the magnetic field induced birefringence (Cotton-Mouton effect), to obtain estimates of magnetizability anisotropies. Two existing semiclassical theories of the effect lead to different numerical results for the physical observable, i.e. the anisotropy of the refractive index. We discuss the results obtained within these two formulations for rare gas atoms, non-dipolar and dipolar small linear molecules employing Coupled Cluster and Coupled Cluster Response theory, a state-of-the-art method developed in the last decade and which currently constitutes one of the most accurate tools available to determine optical properties.