PC GAMESS/Firefly-related discussion club

Pedro Silva
pedros@ufp.pt

>1) is it logical to use molecular orbitals generated from STO-3G runs (with SCFTYP=UHF in hartree fock method) as a starting orbital for my hartree fock open shell calculations using the same method but at 6-31G**?


No... In PcGamess your input guess orbitals must be of the same basis set you want to converge.

>2) Is it alright to use the orbitals (for both open shell and close shell) from hartree fock calculations as a guess orbitals for B3LYP and MP2 single point energy calculation given that the basis set use is the same for the three calculations.

Yes

>3) using only SCFTYP=UHF (for open shell) with the following inputs,
>$SCF �DAMP=.false. DEM=.false. DIIS=.false. DIRSCF=.true. � � � � � � � � � �
> � � � � �EXTRAP=.true. RSTRCT=.false. SHIFT=.false. SOSCF=.true.
>what are your other recommendations for faster and efficient SCF convergence?

>4) is the single point UHF calculation (UBLYP/6-31G** with GUESS=HUCKEL) that converge after long period (about 3 days and iteration of about more than 500) is a sign or indication of wrong MO'S???

UHF convergence is most often helped by mixing the HOMO and LUMO guess orbitals. This is done with:

$guess mix=.t. $end