Firefly and PC GAMESS-related discussion club

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tri_xy@libero.it

i managed to calculate Raman activities with firefly, but i'm not sure that i'm using the correct approach, and the best performing one in terms of copmuting time.
As an example, for Benzene i first run an input file for geometry optimization and frequency analysis, and then a Raman type run.

The geometry optimization input file is like the following:

$CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE MAXIT=300 MULT=1 COORD=UNIQUE $END
! $CONTRL EXETYP=CHECK
$SYSTEM TIMLIM=600 MEMORY=3932160 $END
$BASIS GBASIS=STO NGAUSS=6 $END
$SCF DIRSCF=.TRUE. FDIFF=.FALSE. NCONV=8 $END
$STATPT OPTTOL=1e-006 NSTEP=500 HESS=CALC IHREP=1 HSSEND=.TRUE. $END
$FORCE VIBANL=.TRUE. $END
$DATA
benzene
Dnh 6

C     6.0     1.39499998    -0.00000     0.00000000
H     1.0     2.49469995    -0.0000     0.00000000
$END


From the resulting output file i copy the $VEC group (that should be the one for the optimized geometry) and the $HESS group calculated for the vibrational analysis and paste both the groups in the following ipnut file for Raman activity:

$CONTRL SCFTYP=RHF RUNTYP=RAMAN EXETYP=RUN MAXIT=300 MULT=1 $END
$SYSTEM TIMLIM=36000 MEMORY=2621440 $END
$BASIS GBASIS=STO NGAUSS=6 $END
$GUESS GUESS=MOREAD NORB=36 $END
$SCF DIRSCF=.TRUE. NCONV=8 $END
$DATA
benzene raman
DNH 6

C     6.0     1.38585     0.00000     0.00000
H     1.0     2.46452     0.00000     0.00000
$END

$VEC
...  
this $VEC group is copied from the former output file
...
$END

$HESS
ENERGY IS....
...
this $HESS group is copied from the former output file
...
$END


At the end i obtain Raman and IR lines, but i think that some part of the calculation is made twice. In fact at the end of the geometry-optimization run, i have already the IR lines (but not the Raman ones) and $HESS group.
But when i start the Raman calculation, i'm not sure that Firefly is starting from the $HESS group that i copied in the input file and i have the doubt that it is performing again the vibrational analysis from the beginning.

Can you help me to understand better how manage Raman lines calculations? and more in general vibrational analysis?
do you have some suggestions about the correction factors to be used for Raman and IR lines?

Thanks a lot for your help..