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Title: Why is MP2-Water "Cooler" and "Denser" than DFT-Water?

To maintain water in the liquid phase at the correct (1 g/cm3) density during first-principles simulations, density-functional theory (DFT) with a dispersionless generalized-gradient-approximation (GGA) functional requires a much higher temperature and pressure than the ambient conditions. Conversely, ab initio second-order many-body perturbation (MP2) calculations of liquid water performed by Del Ben et al. [J. Chem. Phys. Lett. 4, 3753 (2013); J. Chem. Phys. 143, 054506 (2015)] and by us [Willow et al., Sci. Rep. 5, 14358 (2015)] required a lower temperature and a negative pressure than DFT to keep water liquid. Here, we present a unifying explanation of these trends derived from classical water simulations using a polarizable force field with different sets of parameters. We show that the calculated temperature and pressure of the liquid phase are strongly correlated with the polarizability of water and the dispersion interaction, respectively. In DFT/GGA, the polarizability and thus the induced dipole moments and the hydrogen-bond strength are all overestimated. This hinders the rotational motion of molecules and requires a higher temperature for water to be liquid. In MP2 and DFT/GGA, the dispersion interaction is stronger and weaker (or lacking), respectively. This explains why liquid water contracts uniformly and becomes too dense inmore » MP2, whereas the opposite is the case for dispersionless DFT/GGA.« less
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Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1948-7185; KC0301050
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry Letters; Journal Volume: 7; Journal Issue: 4
American Chemical Society
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
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Country of Publication:
United States