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Velocity echoes in water


Hamm, Peter (2019). Velocity echoes in water. Journal of Chemical Physics, 151(5):054505.

Abstract

A three-point velocity correlation function v(t(1) + t(2))v2(t(1))v(0) is introduced for a better understanding of the recent 2D-Raman-THz spectroscopy of the intermolecular degrees of freedoms of water and aqueous salt solutions. This correlation function reveals echoes in the presence of inhomogeneous broadening, which are coined velocity echoes. In analogy to the well-known two-point velocity correlation function v(t)v(0), it reflects the density of states (DOS) of the system under study without having to amend them with transition dipoles and transition polarizabilities. The correlation function can be calculated from equilibrium trajectories and converges extremely quickly. After deriving the theory, the information content of the three-point velocity correlation function is first tested based on a simple harmonic oscillator model with Langevin dynamics. Subsequently, velocity echoes of TIP4P/2005 water are calculated as a function of temperature, covering ambient conditions, the supercooled regime and amorphous ice, as well as upon addition of various salts. The experimentally observed trends can be reproduced qualitatively with the help of computationally very inexpensive molecular dynamics simulations.

Abstract

A three-point velocity correlation function v(t(1) + t(2))v2(t(1))v(0) is introduced for a better understanding of the recent 2D-Raman-THz spectroscopy of the intermolecular degrees of freedoms of water and aqueous salt solutions. This correlation function reveals echoes in the presence of inhomogeneous broadening, which are coined velocity echoes. In analogy to the well-known two-point velocity correlation function v(t)v(0), it reflects the density of states (DOS) of the system under study without having to amend them with transition dipoles and transition polarizabilities. The correlation function can be calculated from equilibrium trajectories and converges extremely quickly. After deriving the theory, the information content of the three-point velocity correlation function is first tested based on a simple harmonic oscillator model with Langevin dynamics. Subsequently, velocity echoes of TIP4P/2005 water are calculated as a function of temperature, covering ambient conditions, the supercooled regime and amorphous ice, as well as upon addition of various salts. The experimentally observed trends can be reproduced qualitatively with the help of computationally very inexpensive molecular dynamics simulations.

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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:Physical and Theoretical Chemistry, General Physics and Astronomy
Language:English
Date:7 August 2019
Deposited On:07 Feb 2020 11:43
Last Modified:07 Apr 2020 07:25
Publisher:American Institute of Physics
ISSN:0021-9606
OA Status:Green
Publisher DOI:https://doi.org/10.1063/1.5112163
Project Information:
  • : FunderSwiss National Science Foundation (SNSF)
  • : Grant ID
  • : Project Title
  • : FunderMaxWater network
  • : Grant ID
  • : Project Title

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