To load an external basis set in Firefly simply include the standard syntax for an external basis set in your input file:
$BASIS extfile=.t. GBASIS=cc-pVTZ $END
and appropriately modify your execution string.
If you are on Windows FiCO is a GUI app to run your jobs that will support loading an external basis set for you.
All of the Dunning basis sets are available for download (see link below) so you would simply need to set the GBASIS such that it matches exactly the name of the basis set within the actual *.lib external basis set file itself that you wish to use.
I hope that this gives you enough to proceed with you jobs. There are actually many other approaches such as to download them yourself from EMSL and then to use Chemcraft to have the basis set punched directly in the input file,...etc.
On Thu Mar 11 '10 10:51am, Gordon wrote
>I would like to learn how to run geo opts using DFT B3LYP cc-pVTZ with FIREFLY (with the upshot being calculation of NMR shieldings, to be performed using WinGamess). Is it possible? When I create the input file for FIREFLY (Gabedit), in the "Basis - Basis set" drop-down menu, I see only "Triple Zeta Valence", which prints to the input as "GBASIS=TZV". Using WinGamess, cc-pVTZ prints to the input as "GBASIS=CCT", so I could guess these basis sets are not equivalent (not sure). I have checked on "http://en.wikipedia.org/wiki/Basis_set_%28chemistry%29", where under the correlation-consistent basis sets, "other split-valence basis sets" are listed, where "TZV" appears, but it is not clear to me if they are equivalent.
>Looking to the Firefly-input pdf, I see the function counts are not the same for TZV as compared with cc-pVTZ. I have looked in all the downloaded FIREFLY sample inputs, and not found an example to go by. Have also seen the MP2/cc-pVTZ for C-60 fullerene on the web-site, but also no mention of "GBASIS=CCT" in the input file. There must be a way to do this. I would appreciate very much if someone would help with this. Yes I can do this using WinGamess already, but I would like to use FIREFLY exclusively, except for NMR shielding calcs.