Removing the barrier to the calculation of activation energies: Diffusion coefficients and reorientation times in liquid water

Abstract

General approaches for directly calculating the temperature dependence of dynamical quantities from simulations at a single temperature are presented. The method is demonstrated for self-diffusion and OH reorientation in liquid water. For quantities which possess an activation energy, e.g., the diffusion coefficient and the reorientation time, the results from the direct calculation are in excellent agreement with those obtained from an Arrhenius plot. However, additional information is obtained, including the decomposition of the contributions to the activation energy. These results are discussed along with prospects for additional applications of the direct approach.

Activation energies and the extended jump model: How temperature affects reorientation and hydrogen-bond exchange dynamics in water

“…For n = 1, the overall jump activation energy, Eq. (19), is effectively the same as that for frame reorientation (Ea,n jump = 3.62±0.05 kcal/mol). How these two combine to predict the OH reorientation activation energy depends on the relative jump and frame timescales as given in Eq.…”

“…Using the calculated activation energies of the jump angle distribution, , and the characteristic jump timescale, Ea,0, the total jump contribution to the OH reorientation activation energy, Ea,n jump , can be calculated from Eq. (19). These are found to be 3.62 ± 0.05, 3.44 ± 0.05, and 3.31 ± 0.05 kcal/mol, respectively, for n = 1, 2, and 3.…”

“…Specifically, the total system energy fluctuation can be decomposed into physically meaningful components, which can be used to determine the contributions to the activation energy for each. 19,[21][22][23][24]52 For example, in the case of the fixed-charge classical MD simulations used in the present work, it is natural to divide the energy fluctuation as δH(0) = δKE(0) + δVLJ(0) + δVCoul(0), (11) where KE is the total kinetic energy and VLJ and VCoul are the total Lennard-Jones and Coulombic potential energies. Using this in Eq.…”

“…8,[15][16][17] The traditional determination from a series of measurements at different temperatures is thus ambiguous and sensitively depends on the chosen temperature interval. This issue was recently addressed by a fluctuation theory approach for dynamics, [18][19][20][21][22][23][24] which permits the calculation of activation energies from molecular dynamics simulations at a single temperature. This method further provides important insight in the activation energy components, and has been successfully applied to a broad range of dynamical processes in water.…”

Examining the Hofmeister Series through Activation Energies: Water Diffusion in Aqueous Alkali-Halide Solutions

“…The present work makes use of a recently developed method, derived from the application of fluctuation theory to dynamics, that has been demonstrated for calculating diffusion coefficient activation energies. [46][47][48][49] Specifically, we have previously shown that the derivative of the M SD(t) with respect to inverse temperature (β) is given by 47…”