Abstract
This paper presents a study of the total mean kinetic energy, ⟨EK⟩, and of individual projections along a given molecular axis, ⟨EK⟩α, for D and O nuclei in D2O, derived using a harmonic model. Our theoretical approach assumes decoupling amongst translational, rotational and vibrational modes. Resulting values of these dynamical quantities are discussed in terms of the anisotropy of the quantum kinetic energy tensor, its relation to the local potential, and deviations from the hypothesis of harmonicity and mode decoupling. Results are compared with corresponding quantities obtained from Deep Inelastic Neutron Scattering experiments performed on liquid and solid D2O, where the short-time dynamics and local environment of D and O atoms were probed. The present study confirms an overall picture where even small changes in the short-range environment of D and O nuclei have a strong influence on the quantum behaviour of heavy water.
Highlights
The microscopic dynamics of liquid water still continues to challenge and attract great interest from theorists and experimentalists due to the fundamental relevance of this system in the biological and physical sciences [1]
Several ab initio Path Integral Molecular Dynamics (PIMD) simulations [15,16,17,18] and Deep Inelastic Neutron Scattering (DINS) experiments supplemented by PIMD simulations [19,20,21,22,23,24,25,26,27,28] have been performed to study the structure and dynamics of liquid water over a wide range of temperatures and pressures to investigate how these are directly influenced by nuclear quantum effects (NQEs)
Similar considerations apply to the rotational modes of frequency ωρ, whose contribution to the kinetic energy is defined by the ratio of moments of inertia ρj = Ij/ j Ij
Summary
The microscopic dynamics of liquid water still continues to challenge and attract great interest from theorists and experimentalists due to the fundamental relevance of this system in the biological and physical sciences [1]. Several ab initio Path Integral Molecular Dynamics (PIMD) simulations [15,16,17,18] and DINS experiments supplemented by PIMD simulations [19,20,21,22,23,24,25,26,27,28] have been performed to study the structure and dynamics of liquid water over a wide range of temperatures and pressures to investigate how these are directly influenced by NQEs. some phenomenological models [29, 30] assuming harmonicity and decoupling amongst translational, rotational and vibrational modes have been used to calculate values of the total mean kinetic energy EK , as well as individual contributions EK α along the three principal axes of the quantum kinetic energy tensor of the anisotropic n(p). These predictions are discussed and compared against data from a previous DINS experiment [8]
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