Quantum effects in liquid water: Path-integral simulations of a flexible and polarizable ab initio model

We examine quantum effects in liquid water at ambient conditions by performing path-integral molecular dynamics simulations of a flexible, polarizable water model that was parameterized from ab initio calculations. The quantum liquid is less structured and has a smaller binding energy, in accord with previous simulations. The difference between the quantum and classical liquid binding energies (∼1.5 kcal/mol) is in reasonable agreement with a simple harmonic model, and is somewhat larger than previous estimates in the literature. Quantum effects do not appear to significantly modify the average induced dipole moment for a polarizable model, although the distribution is broader, especially for the component along the C2 axis of symmetry.