The distance between S and four adjacent C atoms (d_SC_i, i = 1, 2, 3, 4) as a function of the MD simulation time in (a) NVT and (b) NPT ensembles, and the six bond angles in donor center ( ∠ C_iSC_j, i, j = 1, 2, 3, and 4) as a function of the MD simulation time in (c) NVT and (d) NPT ensembles. The calculations are performed with 64-atom supercell.