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I'm trying to run Polarizable Continuum Model (PCM) calculations using the GAMESS(US) software. I'm not that well versed in what exactly these calculations are doing (beyond the whole, 'gas within a solvent cavity' explanation). So I will preface and say the calculations might be working and I am simply not understanding the results.

I am running a simple calculation just to start understanding PCM calculations, so I'm using this input:

! AutoGAMESS Version 1.1.8
!  by Brian C. Ferrari 
!
 $CONTRL SCFTYP=RHF MULT=1 NPRINT=0 COORD=UNIQUE
 RUNTYP=HESSIAN ICUT=12 ITOL=25 DFTTYP=B3LYP
 MAXIT=200 QMTTOL=1E-7 ICHARG=0 ISPHER=1 $END
 $SYSTEM MWORDS=800 MEMDDI=800 $END
 $STATPT OPTTOL=1E-6 NSTEP=200 $END
 $PCM SOLVNT=CH3OH $END
 $FORCE METHOD=SEMINUM NVIB=2 PROJCT=.TRUE. $END
 $SCF DIRSCF=.TRUE. FDIFF=.FALSE. CONV=1d-7 $END
 $DFT JANS=2 $END
 $BASIS GBASIS=CCT $END
 $DATA
AutoGAMESS COx Energetics
Cnv 4,

 C           6.0   0.0000000000   0.0000000000   0.5267400687
 O           8.0   0.0000000000   0.0000000000  -0.5996000687
$END

The calculation terminates normally but the results it prints out are the following:

  MODE FREQ(CM**-1)  SYMMETRY  RED. MASS  IR INTENS.
     1       0.000    A       12.000000    0.001636
     2       0.000    A       12.000000    0.001636
     3       0.000    A       12.000000    1.444876
     4       0.000    A       15.994910    0.001228
     5       0.000    A       15.994910    0.001227
     6       0.000    A       15.994910    1.084002

This seems like garbage to me, since the frequencies are all 0 but there are some IR intensities. Which leaves me wondering what is going wrong to cause this error in the calculation? What should I change in the input file?

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    $\begingroup$ For the matter at hand: These low lying modes correspond to rotation and translation; I was always under the impression that gamess does project them out. The intensities may well be numerical noise, after all you are using a lot of approximations. I don't think we have many gamess experts here, so it might be a while before you get a proper answer. $\endgroup$ – Martin - マーチン♦ Jan 2 at 0:40
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    $\begingroup$ I believe Martin is on the right track. With projct=.True., it should project all the translations and rotations to have zero frequency. However, that should only account for the first five in this case, so one of the options used must be making GAMESS project the bottom 6, which is the typical case for nonlinear molecules, rather than correctly zeroing out the first 5 $\endgroup$ – Tyberius Jan 2 at 2:30
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    $\begingroup$ I have found the following on the force keyword: At stationary points, the projection simply eliminates rotational and translational contaminants. At points with non-zero gradients, the projection also ensures that one of the vibrational modes will point along the gradient, so that there are a total of 7 zero frequencies. Could you please check and post the gradient, too. Did you get a message that you have reached a stationary point? For comparison, you could run the calculation without solvent and with analytical derivatives. $\endgroup$ – Martin - マーチン♦ Jan 2 at 11:52
  • $\begingroup$ @Martin-γƒžγƒΌγƒγƒ³ With the PCM calculation it says it has not reached a stationary point however for the non-PCM calculation with the same parameters it does reach a stationary point. I'll try putting stricter convergence criteria on it and see if that helps. $\endgroup$ – Cavenfish Jan 3 at 20:05
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    $\begingroup$ Well, that at least explains the extra mode. Using tighter convergence is often a good idea, but check carefully if it oscillates. Tighter scf convergence might also help, and a larger grid will almost always improve the calculation (at a cost of course). As long as there is no proper answer, you might also want to update the post. To avoid lengthy discussions here, you can also find me in Chemistry Chat. Good luck! $\endgroup$ – Martin - マーチン♦ Jan 3 at 20:26

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