Kinetic energy of protons in ice Ih and water: A path integral study

Ramı́rez, Rafael; Herrero, Carlos P.

doi:10.1103/physrevb.84.064130

Cited by 40 publications

(30 citation statements)

References 46 publications

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“…keywords: deep inelastic neutron scattering; ab initio path integral molecular dynamics; particle momentum distribution A large number of experimental and theoretical dynamical studies of liquid water near the triple point are available in literature [1][2][3][4][5][6][7][8][9] nevertheless an full and accurate characterization of hydrogen dynamics is still lacking. The latter is of vital importance for clarifying thermodynamic properties and the key to expand our understanding of some of the mysterious characteristics of water, supercooled water (SW) and glassy water, the latter being its viscous counterparts, known as amorphous ice.…”

Section: Toc Graphicmentioning

confidence: 99%

Direct Measurements of Quantum Kinetic Energy Tensor in Stable and Metastable Water near the Triple Point: An Experimental Benchmark

Andreani

Romanelli

Senesi

2016

J. Phys. Chem. Lett.

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This study presents the first direct and quantitative measurement of the nuclear momentum distribution anisotropy and the quantum kinetic energy tensor in stable and metastable (supercooled) water near its triple point, using deep inelastic neutron scattering (DINS). From the experimental spectra, accurate line shapes of the hydrogen momentum distributions are derived using an anisotropic Gaussian and a model-independent framework. The experimental results, benchmarked with those obtained for the solid phase, provide the state of the art directional values of the hydrogen mean kinetic energy in metastable water. The determinations of the direction kinetic energies in the supercooled phase, provide accurate and quantitative measurements of these dynamical observables in metastable and stable phases, that is, key insight in the physical mechanisms of the hydrogen quantum state in both disordered and polycrystalline systems. The remarkable findings of this study establish novel insight into further expand the capacity and accuracy of DINS investigations of the nuclear quantum effects in water and represent reference experimental values for theoretical investigations.A large number of experimental and theoretical dynamical studies of liquid water near the triple point are available in literature; 1−9 nevertheless, a full and accurate characterization of hydrogen dynamics is still lacking. The latter is of vital importance for clarifying thermodynamic properties and the key to expand our understanding of some of the mysterious characteristics of water, supercooled water (SW), and glassy water, the latter being its viscous counterparts, known as amorphous ice. 10 Nuclear quantum effects (NQEs) play an important role in water, ice, and hydrogen-bonded systems and directly influence their microscopic structure and dynamical properties. In most of these cases, the hydrogen atoms are localized in potential wells with pronounced zero point motion. The equilibrium hydrogen dynamics is reflected in the quantum momentum distribution, n(p), a quantity which provides complementary information to what is garnered from diffraction techniques. Because of NQEs, n(p) markedly differs from the classical Maxwell−Boltzmann distribution, being determined almost entirely by the quantum mechanics of the vibrational ground state properties. 11−17 This makes n(p) a highly sensitive probe of the local environment, fingerprinting any changes occurring both in the structure of the hydrogen-bonded network as well as in the local symmetry. Thus, n(p) together with the mean kinetic energy, ⟨E K ⟩, provide key insights into the hydrogen local environment to rationalize the puzzling feature of liquid water near the triple point. DINS is the unique experimental technique that directly access the n(p). 18 The basic principles of data interpretation of the DINS technique are based on the validity of the impulse approximation (IA), 19 which is exact in the limit of infinite momentum transfer, ℏq. 20,21 Within the IA, the inelastic neutron sc...

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Section: Toc Graphicmentioning

confidence: 99%

Direct Measurements of Quantum Kinetic Energy Tensor in Stable and Metastable Water near the Triple Point: An Experimental Benchmark

Andreani

Romanelli

Senesi

2016

J. Phys. Chem. Lett.

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“…This condition has been applied in previous water and ice simulations with the same model potential. 30,31,[44][45][46] A staging transformation was employed for the bead coordinates. This linear transformation was introduced to diagonalize the harmonic coupling between neighboring beads.…”

Section: Computational Conditionsmentioning

confidence: 99%

“…In addition, the kinetic energy obtained for ice Ih and water from NPT simulations at zero pressure is also plotted. 31,44 The quantum kinetic energy of the droplets displays a monotonous temperature dependence without apparent discrimination between its solid or liquid behavior between 50 and 350 K (see Fig. 7(a)).…”

Section: A Internal Energymentioning

confidence: 99%

Ice and water droplets on graphite: A comparison of quantum and classical simulations

Ramı́rez

Singh

Müller‐Plathe

et al. 2014

The Journal of Chemical Physics

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Ice and water droplets on graphite have been studied by quantum path integral and classical molecular dynamics simulations. The point-charge q-TIP4P/F potential was used to model the interaction between flexible water molecules, while the water-graphite interaction was described by a Lennard-Jones potential previously used to reproduce the macroscopic contact angle of water droplets on graphite. Several energetic and structural properties of water droplets with sizes between 10(2) and 10(3) molecules were analyzed in a temperature interval of 50-350 K. The vibrational density of states of crystalline and amorphous ice drops was correlated to the one of ice Ih to assess the influence of the droplet interface and molecular disorder on the vibrational properties. The average distance of covalent OH bonds is found 0.01 Å larger in the quantum limit than in the classical one. The OO distances are elongated by 0.03 Å in the quantum simulations at 50 K. Bond distance fluctuations are large as a consequence of the zero-point vibrations. The analysis of the H-bond network shows that the liquid droplet is more structured in the classical limit than in the quantum case. The average kinetic and potential energy of the ice and water droplets on graphite has been compared with the values of ice Ih and liquid water as a function of temperature. The droplet kinetic energy shows a temperature dependence similar to the one of liquid water, without apparent discontinuity at temperatures where the droplet is solid. However, the droplet potential energy becomes significantly larger than the one of ice or water at the same temperature. In the quantum limit, the ice droplet is more expanded than in a classical description. Liquid droplets display identical density profiles and liquid-vapor interfaces in the quantum and classical limits. The value of the contact angle is not influenced by quantum effects. Contact angles of droplets decrease as the size of the water droplet increases which implies a positive sign of the line tension of the droplet.

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“…Early reports of large anomalies in the temperature dependence of proton kinetic energy in supercooled water 8,9 have not been reproduced in path integral simulations using empirical forcefields, 10 and have been considerably reassessed in subsequent measurements. 11 An early study of this discrepancy based on vibrational self-consistent field calculations came to the conclusion that softening of the OH stretch due to electrostatic interactions could not reproduce the experimental momentum distribution at room temperature and below.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy of the Proton Momentum Distribution in Water

2018

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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.

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Kinetic energy of protons in ice Ih and water: A path integral study

Cited by 40 publications

References 46 publications

Direct Measurements of Quantum Kinetic Energy Tensor in Stable and Metastable Water near the Triple Point: An Experimental Benchmark

Direct Measurements of Quantum Kinetic Energy Tensor in Stable and Metastable Water near the Triple Point: An Experimental Benchmark

Ice and water droplets on graphite: A comparison of quantum and classical simulations

Anisotropy of the Proton Momentum Distribution in Water

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