Derivation and evaluation of a flexible SPC model for liquid water

Molecular dynamics simulations of a new flexible water model are presented. The potential function is based on the simple point charge (SPC) model combined with an accurate experimental quartic intramolecular potential (CCL). This potential not only reproduces the key structural, dynamical and thermodynamical properties of liquid water, but also generates the correct values for both the absolute O-H vibrational frequency and the gas-to-liquid frequency shift. Thus, the model yields a value of ca. 3420 cm(-1) for the peak maximum of the anharmonic OH stretching band for liquid water (experiment 3400 cm(-1)) and a corresponding gas-to-liquid downshift of -300 cm(-1) (experiment -310 cm(-1)). The paper also emphasizes the importance of parameterizing correctly both the harmonic and anharmonic force constants in the gas-phase when developing flexible water models to be used in the liquid state. (C) 2004 Elsevier B.V. All rights reserved.