The Cotton - Mouton effect of liquid water. Part II: The semi-continuum model

We present gauge-origin independent calculations of the Cotton - Mouton effect of liquid water. The liquid is represented by a semi-continuum model such that the central molecule is surrounded by its first solvation shell, which explicitly accounts for the strong interaction between the water molecule of interest and its closest neighbors. The long-range interactions with the solvent are modeled by a dielectric continuum surrounding the water molecule and the first solvation shell. We employ large basis sets, using London atomic orbitals in order to obtain gauge-origin independent results close to the Hartree - Fock limit. It is demonstrated that the direct interaction between neighboring molecules leads to a large effect on the calculated Cotton - Mouton constant, which undergoes a sign change from the gas to liquid phase, as observed previously for the linear electro-optical effect [K. V. Mikkelsen et al., J. Chem. Phys 102, 9362 (1995)]. Our best estimate for the molar Cotton-Mouton constant, -38.1 · 10-20G-2cm3mol-1(corrected for local field effects), is in reasonable agreement with the experimental value of -118( 15) · 10-20G-2cm3mol-1. We expect that the remaining discrepancy is mainly due to an inadequate treatment of electron correlation. © 1998 American Institute of Physics.