I want to calculate diffusion coefficient for a material after doping using VASP but I don't know how to change POSCAR file. what changes should I put in POSCAR file for Li10‑xSnP2S12‑xClx
You need to build a supercell to meet the doping content. Note that the calculated amount of VASP is positively correlated with the number of atoms. Too many atoms will take too much time. After you modified the crystal data of .cif through VESTA software, POSCAR can obtain through export from VESTA software.