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Ab initio molecular dynamics study of collective excitations in liquid H2O and D2O: Effect of dispersion corrections - Zurich Open Repository and Archive


Bryk, Taras; Seitsonen, Ari (2016). Ab initio molecular dynamics study of collective excitations in liquid H2O and D2O: Effect of dispersion corrections. Condensed Matter Physics, 19(2):23604.

Abstract

The collective dynamics in liquid water is an active research topic experimentally, theoretically and via simulations. Here, ab initio molecular dynamics simulations are reported in heavy and ordinary water at temperature 323.15 K, or 50oC. The simulations in heavy water were performed both with and without dispersion corrections. We found that the dispersion correction (DFT-D3) changes the relaxation of density-density time correlation functions from a slow, typical of a supercooled state, to exponential decay behaviour of regular liquids. This implies an essential reduction of the melting point of ice in simulations with DFT-D3. Analysis of longitudinal (L) and transverse (T) current spectral functions allowed us to estimate the dispersions of acoustic and optic collective excitations and to observe the L-T mixing effect. The dispersion correction shifts the L and T optic (O) modes to lower frequencies and provides by almost thirty per cent smaller gap between the longest-wavelength LO and TO excitations, which can be a consequence of a larger effective high-frequency dielectric permittivity in simulations with dispersion corrections. Simulation in ordinary water with the dispersion correction results in frequencies of optic excitations higher than in D2O, and in a long-wavelength LO-TO gap of 24 ps-1 (127 cm-1).

Abstract

The collective dynamics in liquid water is an active research topic experimentally, theoretically and via simulations. Here, ab initio molecular dynamics simulations are reported in heavy and ordinary water at temperature 323.15 K, or 50oC. The simulations in heavy water were performed both with and without dispersion corrections. We found that the dispersion correction (DFT-D3) changes the relaxation of density-density time correlation functions from a slow, typical of a supercooled state, to exponential decay behaviour of regular liquids. This implies an essential reduction of the melting point of ice in simulations with DFT-D3. Analysis of longitudinal (L) and transverse (T) current spectral functions allowed us to estimate the dispersions of acoustic and optic collective excitations and to observe the L-T mixing effect. The dispersion correction shifts the L and T optic (O) modes to lower frequencies and provides by almost thirty per cent smaller gap between the longest-wavelength LO and TO excitations, which can be a consequence of a larger effective high-frequency dielectric permittivity in simulations with dispersion corrections. Simulation in ordinary water with the dispersion correction results in frequencies of optic excitations higher than in D2O, and in a long-wavelength LO-TO gap of 24 ps-1 (127 cm-1).

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Uncontrolled Keywords:collective excitations, optic modes, water, heavy water, van der Waals corrections, ab initio molecular dynamics
Language:English
Date:2016
Deposited On:16 Dec 2016 10:17
Last Modified:16 Dec 2016 11:46
Publisher:Institute for Condensed Matter Physics
ISSN:1607-324X
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.5488/CMP.19.23604
Other Identification Number:1603.07144

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