On the Orientational Structure and Dielectric Properties of Water. A Comparison of ST2 and MCY Potential

Molecular dynamics simulations involving 500 and 1000 molecules are reported for the ST2 [7] and MCY [8] potential. The thermodynamic state corresponds to a density of ρ = 1 gcm −3 and a temperature around T = 400 K. Although traditionally used, atom‐atom correlation functions are found to be inappropriate for a detailed discussion of the orientational structure. Therefore the complete analysis is based on the full angle‐dependent pair correlation function g ( R , Ω 1 , Ω 2 , Ω 12 ). In the case of MCY considerable distortion of the ideal tetrahedral picture is observed. Although a collective property, the Kirkwood g ‐factor turns out to be a sensitive probe of the input potentials and differs by a factor of 3 as a consequence of the angle‐dependent short‐range forces of the MCY potential. The mutual consistence of local and asymptotic dielectric properties is carefully examined. Thus a unique dielectric constant of ϵ MCY = 30 ± 5 is derived. Possible refinements of the MCY potential are discussed in order to bring the computed ϵ MCY closer to the experimental value ϵ exp = 51.