Generate .fchk file after the completion of job

If the opt job has been completed successfully and you did not request for .fchk file, then how to generate the .fchk file? Is it necessary to submit a new single point with “IQMOL_FCHK = TRUE”?

yes. if you’ve saved the scratch files you could read in the guess to speed things up, but there’s no other way to get .fchk