In this work, we have performed extensive density functional theory (DFT) based <i>ab initio</i> path-integral molecular dynamics (PI-AIMD) simulations of liquid water at ambient conditions in both the canonical (NVT) and isothermal-isobaric (NpT) ensembles to investigate the individual and collective importance of exact exchange, non-local van der Waals (dispersion) interactions, and nuclear quantum effects on the structural properties of liquid water. PI-AIMD simulations which systematically account for these effects result in structural properties which are in excellent agreement with experiment and a liquid water having an equilibrium density within a few percent of the experimental value of approximately 1 g/cm^3. A detailed analysis of the local environment in ambient liquid water has revealed that individual water molecules naturally fluctuate between spatially high- and low-density environments and the corresponding inherent potential energy surface (IPES) is bimodal, consistent with the existence of polymorphism in the amorphous phases of water. With these findings, the methodology presented herein overcomes the well-known limitations of semi-local DFT and provides a detailed and accurate microscopic description of ambient liquid water.

Microscopic structure, equilibrium density, and local environment in liquid water: A highly accurate ab initio path-integral molecular dynamics study

249th National Meeting (2015)

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