Abstract
Although the electrical conductivity of an electrolyte can be estimated from the molecular dynamics trajectory, it is often a challenging task because of the need to obtain a substantial amount of data to ensure sufficient averaging. Here, we present an analysis on the convergence of results with the number of simulated trajectories. A series of molecular dynamics simulations have been performed for a model electrolyte (NaCl in water) and the Einstein relation has been used to calculate the electrical conductivity. The standard deviation of the conductivity estimates is relatively large compared to the mean value, and it has been shown that the off-diagonal contributions to the collective displacement of ions are responsible for large deviations between systems. It has been found that about 40 independent MD simulations may be required to reduce the errors. A procedure to improve the final estimate of the conductivity has been proposed.
Highlights
Equilibrium molecular dynamics (MD) simulations are today a standard tool for modeling systems in the condensed phase and liquids in particular.[1,2] MD delivers invaluable information on the structure and dynamics of complex molecular systems; it is frequently used in various disciplines ranging from material science to biochemistry.A fast growing area of the application of MD is the research on power sources including studies on physicochemical properties of electrolytes
In order to improve the accuracy of properties estimated from the MD simulations, one may invest the computational effort in increasing the system size, the length of the MD trajectory, or the number of realizations of the system
We have investigated the issue of calculations of the electrical conductivity from the MD simulations
Summary
A fast growing area of the application of MD is the research on power sources including studies on physicochemical properties of electrolytes. In this context, obtaining estimates of transport-related properties of the electrolyte, diffusion coefficients and electrical conductivity, is of great importance. Appropriate averaging of data is necessary in order to reliably calculate desired values. It is easier to achieve sufficient averaging in the case of diffusion coefficients because it may be improved by increase in the size of studied systems. Issues related to the derivation of diffusion coefficients have already been discussed in several studies.[3−5]
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