How do I convert files from an old Gaussian version to another version?

Almost all old Gaussian input files are valid for later versions. However, the format for checkpoint files has been changed several times. Using Gaussian09 for example, the following command sequence performs a checkpoint conversion in place: % cp -p mycalc.chk mycalc.chk.original % module load g09 % c8609 mycalc.chk The Gaussian09 module must be loaded to access the c8609 utility. The mycalc.chk file will be rewritten in Gaussian09 format. For reference, see http://www.gaussian.com/g_ur/m_utils.htm. The command c8609*.chk converts only the first file, so you must convert each checkpoint file separately. The conversion utility program name contains the version, so for the Gaussian03 module the program name is c8603.