Anisotropy of the Proton Momentum Distribution in Water

Venkat Kapil*, Alice Cuzzocrea, Michele Ceriotti

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

12 Citations (Scopus)


One of the many peculiar properties of water is the pronounced deviation of the proton momentum distribution from Maxwell-Boltzmann behavior. This deviation from the classical limit is a manifestation of the quantum mechanical nature of protons. Its extent, which can be probed directly by deep inelastic neutron scattering experiments, gives important insight on the potential of mean force felt by H atoms. The determination of the full distribution of particle momenta, however, is a real tour de force for both experiments and theory, which has led to unresolved discrepancies between the two. In this study, we present comprehensive, fully converged momentum distributions for water at several thermodynamic state points, focusing on the components that cannot be described in terms of a scalar contribution to the quantum kinetic energy, and providing a benchmark that can serve as a reference for future simulations and experiments. In doing so, we also introduce a number of technical developments that simplify and accelerate greatly the calculation of momentum distributions by means of atomistic simulations.

Original languageEnglish
Pages (from-to)6048-6054
Number of pages7
JournalThe Journal of physical chemistry B
Issue number22
Publication statusPublished - 7 Jun 2018
Externally publishedYes


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