Examining the Role of Different Molecular Interactions on Activation Energies and Activation Volumes in Liquid Water

There
are a large number of force fields available to model water
in molecular dynamics simulations, which each have their own strengths
and weaknesses in describing the behavior of the liquid. One particular
weakness in many of these models is their description of dynamics
away from ambient conditions, where their ability to reproduce measurements
is mixed. To investigate this issue, we use the recently developed
fluctuation theory for dynamics to directly evaluate measures of the
local temperature and pressure dependence: the activation energy and
the activation volume. We examine these activation parameters for
hydrogen-bond jump exchange times, OH reorientation times, and diffusion
coefficients calculated from the SPC/E, SPC/Fw, TIP3P-PME, TIP3P-PME/Fw,
OPC3, TIP4P/2005, TIP4P/Ew, E3B2, and E3B3 water models. Activation
energy decompositions available through the fluctuation theory approach
provide mechanistic insight into the origins of different temperature
dependences between the various models, as well as the influence of
three-body effects and flexibility.