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Analysis of the statistical and convergence properties of ionic transport
coefficients with application to the solid electrolyte
Li2OHCl
Jason David Howard and N. A. W. Holzwarth
Solid State Ionics 325 80-89 (2018)
(local copy)
The challenge of computing ionic transport coefficients from first principles
is to achieve the necessary convergence with respect to system size,
simulation time, and
configurational sampling. Unfortunately current computer resources are not
yet available for such convergence studies at the fully first principles level.
In this work,
a lattice kinetic Monte Carlo model is used to study the convergence properties
of transport coefficients, using the Li sub-lattice of the Li ion electrolyte
Li2OHCl as an
example system. The specific transport coefficients representing tracer
diffusion, effective diffusion, and mobility are carefully studied for
their convergence
properties. Additionally, ion pair correlations of the effective diffusion
are recast as a sum over events which allows for a detailed study of the
nature of the
correlation in terms of time and spatial separation. This experience
suggests a general method of performing simulations by using first a
kinetic Monte Carlo model
followed by a first principles molecular dynamics study. For the
Li2OHCl system, the kinetic Monte Carlo results provide both
a reference for the Haven ratio due to
purely geometric effects and a measure of the computational effort
needed to obtain meaningful molecular dynamics results. The combination
of the two methods
provides further evidence of anti-correlated Li-ion motion in this
system as predicted in a previous study.