Competing quantum effects in the dynamics of a flexible water model

Abstract

Numerous studies have identified large quantum mechanical effects in the dynamics of liquid water. In this paper, we suggest that these effects may have been overestimated due to the use of rigid water models and flexible models in which the intramolecular interactions were described using simple harmonic functions. To demonstrate this, we introduce a new simple point charge model for liquid water, q-TIP4P/F, in which the O--H stretches are described by Morse-type functions. We have parameterized this model to give the correct liquid structure, diffusion coefficient, and infra-red absorption frequencies in quantum (path integral-based) simulations. By comparing classical and quantum simulations of the liquid, we find that quantum mechanical fluctuations increase the rates of translational diffusion and orientational relaxation in our model by a factor of around 1.15. This effect is much smaller than that observed in all previous simulations of simple empirical water models, which have found a quantum effect of at least 1.4 regardless of the quantum simulation method or the water model employed. The small quantum effect in our model is a result of two competing phenomena. Intermolecular zero point energy and tunneling effects destabilize the hydrogen bonding network, leading to a less viscous liquid with a larger diffusion coefficient. However this is offset by intramolecular zero point motion, which changes the average water monomer geometry resulting in a larger dipole moment, stronger intermolecular interactions, and slower diffusion. We end by suggesting, on the basis of simulations of other potential energy models, that the small quantum effect we find in the diffusion coefficient is associated with the ability of our model to produce a single broad O-H stretching band in the infra-red absorption spectrum.

Published in JCP

Cited by in corpus (26)

• How van der Waals interactions determine the unique properties of water
• Efficient stochastic thermostatting of path integral molecular dynamics
• Symmetry-Adapted Machine-Learning for Tensorial Properties of Atomistic Systems
• How to remove the spurious resonances from ring polymer molecular dynamics
• On the accuracy of the MB-pol many-body potential for water: Interaction energies, vibrational frequencies, and classical thermodynamic and dynamical properties from clusters to liquid water and ice
• Nuclear quantum effects in solids using a colored-noise thermostat
• Efficient first-principles calculation of the quantum kinetic energy and momentum distribution of nuclei
• Accelerating the convergence of path integral dynamics with a generalized Langevin equation
• On the Consistency of Approximate Quantum Dynamics Simulation Methods for Vibrational Spectra in the Condensed Phase
• Quantum fluctuations and isotope effects in ab initio descriptions of water
• Molecular dynamics simulations of the ice temperature dependence of water ice photodesorption
• Water: one molecule, two surfaces, one mistake
• Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base Pairs
• Stability of Complex Biomolecular Structures: Vander Waals, Hydrogen Bond Cooperativity, and Nuclear Quantum Effects
• Ab-initio molecular dynamics simulation of liquid water by Quantum Monte Carlo
• Quasi-harmonic approximation of thermodynamic properties of ice Ih, II, and III
• Nuclear quantum effects in water exchange around lithium and fluoride ions
• Improved Ab Initio Molecular Dynamics by Minimal Biasing with Experimental Data
• Feynman Diagram Description of 2D-Raman-THz Spectroscopy Applied to Water
• From Classical to Quantum and Back: Hamiltonian Adaptive Resolution Path Integral, Ring Polymer, and Centroid Molecular Dynamics
• The phase diagram of ice Ih, II, and III: a quasi-harmonic study
• High-density amorphous ice: A path-integral simulation
• Molecular packing and chemical association in liquid water simulated using ab initio hybrid Monte Carlo and different exchange-correlation functionals
• Electronic coarse graining enhances the predictive power of molecular simulation allowing challenges in water physics to be addressed
• Quantum kinetic energy and isotope fractionation in aqueous ionic solutions
• Role of quantum fluctuations in structural dynamics of liquids of light molecules