Molecular mass

[bgpeyton]

Psi4 does not have a built-in function for getting the molecular weight of a molecule (or in my case, a fragment). I've implemented a code to do this by grabbing the individual masses of the atoms and summing them, storing the sum in the database.

One snag was I had to be sure not to count the masses of atoms that were ghosted. This makes me wonder whether or not optrot.cc within PSI4 is properly accounting for the mass. This needs to be checked.