where < r 2 (t) > is the two-dimensional mean squared displacement (MSD) of phosphorus atoms, D is the diffusion coeficient, and t is the simulation time. A time interval between 100 ns and 150 ns was used for the linear it to obtain D. The error estimate was done by calculating the difference of the diffusion coeficients obtained from the two halves of the it interval, as implemented in the "GROMACS msd" tool.