RATIONALIZATION OF THE DIELECTRIC-PROPERTIES OF COMMON 3-SITE WATER MODELS IN TERMS OF THEIR FORCE-FIELD PARAMETERS

The dielectric properties (static dielectric constant epsilon(0), Deby e relaxation time tau(D) and distance dependent Kirkwood G-factor G(k) (R)) of commonly used three-site water models (the ''simple point char ge'' models SPC and SPC/E, as well as the ''transferable intermolecula r potentials with three point charges'' TIP3P and its CHARMM modified variant TTP3P(mod)) were evaluated from 2 ns molecular dynamics simula tions using the Ewald summation method to compute the electrostatic in teractions. The results for SPC (epsilon(0) = 65 +/- 5, tau(D) = 7.6 /- 0.8 ps) and SPC/E (epsilon(0) = 68 +/- 6, tau(D) = 12.1 +/- 1.3 ps) are in good agreement with the literature; for TIP3P (TIP3P(mod)) we obtained a dielectric constant epsilon(0) = 97 +/- 7 (97 +/- 6) and a Debye relaxation time tau(D) = 7.3 +/- 0.7 ps (6.9 +/- 0.6 ps). The su rprisingly large differences in Eo were rationalized by an investigati on of the relationship between the force field parameters and the diel ectric properties. Based on simulations of hybrid SPC/TIP3P models, th e HOH bond angle was identified as the determining factor of the diele ctric constant. By contrast, tau(D) was shown to depend mainly on the OH bond length and the partial charges; the HOH angle is of secondary importance. The role of the HOH angle is clarified by a comparison of the orientational correlation functions of the water models. (C) 1998 American Institute of Physics.