Using cellpar instead of cell is dangerous for writing pdb file
I've built an atoms models from xyz and cell. When I write it into pdb format, the structure was not I want. The reason is that the used cell is a rotated hexagonal cell instead of a standard one. Only when it is written into the format that contain whole cell information (e.g. vasp-POSCAR, xsf ) can give right structure. Maybe the solution is that all positions should be rotated to standard pbc cell when using ase.geometry.cell_to_cellpar.