Finally, an FPMD simulation was performed based on Density Functional Theory (DFT) using the Vienna Ab Initio Simulation Package (VASP) to compare the structure with that obtained using the force-field-based MD simulation. We performed FPMD simulations in an NPT ensemble, in which temperature and pressure were controlled using Langevin thermostating and barostating techniques. The plane-wave basis sets and projectoraugmented-wave pseudopotentials were used under periodic boundary conditions. An energy cutoff of 320 eV was used; integrals over the Brillouin zone were performed only at the Γ-point. The simulated super-cell consisted of 2× 1× 1 unit cells with a total of 88 atoms. The FPMD simulation was performed at 800 K for 1-ps equilibration and 2-ps sampling with a time step of 1 fs.