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Gordon
gordon.driver@abo.fi

thanks very much for the suggestions. I'll start playing around with the $MP2 group as well.

Cheers,
Gordon

On Mon May 17 '10 2:40pm, Richard wrote
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>You probably need to decrease opttol to say 1d-6 - see also the recommendations at http://classic.chem.msu.su/gran/gamess/mp2grd.htmlhttp://classic.chem.msu.su/gran/gamess/mp2grd.htmlhttp://classic.chem.msu.su/gran/gamess/mp2grd.htmlhttp://classic.chem.msu.su/gran/gamess/mp2grd.html

>Richard

>On Mon May 17 '10 8:10am, Gordon wrote
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>>Dear forum followers,

>>I have been optimising geometries to calculate gas phase proton affinities with FF, using MP2 6-311+G(d,p) which will generally yield calc'd values within +/- 10 kJ/mol of experimental values. Now I am trying the same business using $BASIS NDFUNC=2 NFFUNC=1 NPFUNC=2 DIFFSP=.TRUE. DIFFS=.TRUE. $END. With this I can optimise the geometry, BUT, I also observe a single imaginary frequency. To try to fix this, I then used the same input and included $CONTRL RUNTYP=Optimize ICUT=30 ITOL=30 INTTYP=HONDO $END and $SCF DIRSCF=.TRUE. NCONV=10 FDIFF=.FALSE. $END.  (I have attached the two outputs for the acetate anion here).  I have also tried with ICUT=25, but I obtain the same result.

>>I am not sure what I could do now to get further down the PE well!  Perhaps directed adjustment of these ICUT, ITOL, NCONV values are in order?  After 3 tries I was hoping to receive a suggestion from those who are more knowledgeable.  Perhaps there is another trick to try?

>>I would be most grateful for any suggestions.

>>Cheers,
>>Gordon