This command writes the current model topology (which must have already been created via model.generate_topology() or complete_pdb) to a CHARMM or X-PLOR format PSF file or file handle (see modfile.File()).
PSF files contain information on all atoms in the model and their types, plus all the connectivity (bonds, angles, etc). By default X-PLOR format PSF files are written, in which each atom has a defined type name. These are more flexible than CHARMM format PSF files, in which each atom type is specified numerically.
PSF files are generally required in combination with binary format trajectory files, as written by actions.charmm_trajectory().Example: See actions.charmm_trajectory() command.