_modeller.ModellerError: rdpdb___303E> No atoms were read from the
specified input PDB file, since the starting residue number and/or chain
id in MODEL_SEGMENT (or the alignment file header) was not found;
requested starting position: residue number " ", chain " "; atom file
name: loop.pdb
Specification of an initial model is one way to help the optimizer find
optimal solutions. In principle of course the optimizer will find the
global solution, so the choice of initial model is irrelevant. That
said, the initial model must be in the same format as the models
generated by Modeller - i.e. the same amino acid sequence, residue
numbering and chain IDs.