To be used only with proteins, PDBOUT will cause the geometry to be printed in PDB format. Although the format printed is designed to match that used in the Brookhaven Protein Data Bank, the agreement is not always exact. 

By default, the residue sequence will be that supplied by the data set.  To re-calculate residues, use RESIDUES; that will ignore the residue names supplied by the data set, and re-calculate them using the topology of the system. If this option is used, check that the new residue names are acceptable.  To do this, look in the output file for the section:

If the data set includes comments (lines that start with an asterisk (*)) followed by PDB words such as HEADER, TITLE, COMPOUND, REMARK, etc., these will be printed in the PDB format.  This is very useful in preserving the integrity of the PDB file.

If residues are missing, or if multiple proteins are present, keyword START_RES(text) should be used to indicate this. By default, each chain, or section of chain, will be given a different letter, starting with "A".  This can cause problems, particularly if a chain has a gap in it, because, by default, MOPAC would give the two chain sections different letters.  Chain letters can be explicitly assigned by using CHAIN(text).  These keywords are automatically generated when a PDB file is read in and a MOPAC data set generated.

If hydrogen atoms have been added, these will automatically be put in their correct place in the PDB file, unless NORESEQ is present.

Except for hydrogen atoms, atom labels will not be changed. Label names for hydrogen atoms will be based on the atom the hydrogen is attached to.  This makes proton migrations easier to identify.

A fast way to convert a data-set from MOPAC to PDB format is to use 0SCF and PDBOUT. Also, if a restart file, <file>.res, is present, adding RESTART to the data set will read in the updated geometry and, if 0SCF and PDBOUT are also both present, will immediately print the current geometry in PDB format.