Simulation of liquid water using a high-rank quantum topological electrostatic potential

For the first time a potential based on high-rank atomic multipole moments computed according to quantum chemical topology (QCT) has been used in molecular dynamics simulations. Completing earlier work on the performance of this QCT potential on small gas-phase van der Waals complexes we now focus on the liquid structure of water. Other than the parameter L, which keeps track of the rank of the electrostatic interaction, the current QCT potential contains only two adjustable parameters of the Lennard-Jones type. A system of 216 water molecules was simulated including long-range interactions represented by a high-rank multipolar Ewald summation. High-order multipolar interactions (L = 5) are essential to recover the typical features of a liquid-like structure. Liquid simulations at five different temperatures showed a maximum in the density and a temperature profile that agrees fairly well with experiment. The density of simulated water at 300 K and 1 atm, is about 0.1% off the experimental value, while the calculated potential energy of the liquid is within 3% of the experimental result. The experimental value of the self-diffusion coefficient is underestimated by 35%. The value of C-p is overestimated by 40% and the thermal expansion coefficient alpha by 37%. The calculated correlation coefficients between the calculated QCT profile and the experimental profile of g(OO)(r), g(OH)(r), and g(HH)(r) are 0.976, 0.970, and 0.972, respectively. (C) 2004 Wiley Periodicals, Inc.