On the accurate calculation of the dielectric constant and the diffusion coefficient from molecular dynamics simulations: the case of SPC/E water

摘要

The effect of the applied trajectory length on the convergence of the staticdielectric constant and the self-diffusion coefficient were examined for theSPC/E water model in the NVT ensemble with different system size at 293 K. Verylong simulation times of 6-8 ns were employed in order to track the convergenceof these properties. Temperature dependence and isotope effects, via usingD$_2$O instead of H$_2$O, were also investigated. A simulation for thepolarizable SWM4-DP model was also carried out to compare the effect ofdifferent potential models. Radial distribution functions and the neutronweighted structure factor were also calculated; they were found to beinsensitive to changing the system size in the range of 216-16000 molecules. Onthe other hand, the static dielectric constant and the diffusion coefficientare rather sensitive to the applied trajectory length, system size and themethod of calculation. These latter properties are therefore not appropriatefor assessing, and distinguishing between, potential models of water. It isclearly shown that trajectories shorter than about 6 ns are not sufficient fora sufficiently accurate determination of the dielectric constant of this watermodel.