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Miro Moman
edelmiro.moman@gmail.com

This is the input I used to optimise the geometry:

$CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE $END
$CONTRL MAXIT=200 $END
$CONTRL ICHARG=-1 MULT=1 $END
$SCF DIRSCF=.T. FDIFF=.T. NPUNCH=0 $END
$BASIS GBASIS=N31 NGAUSS=6 NDFUNC=2 NPFUNC=1 DIFFSP=.T. $END
$SYSTEM TIMLIM=99999999999 MEMORY=268435456 $END
$STATPT IFREEZ(1)=16,17,18,46,47,48,61,62,63 $END
$STATPT NSTEP=1000 OPTTOL=0.0005 NPRT=-2 NPUN=-2 $END

In order to make it converge, I first minimised at the HF/6-31G(d) level of theory while freezing some coordinates, then I free all atoms for one step, and then I froze them again. This was not converging and so I started to increase progressively the level of theory until finally it converged at HF/6-31G+(2d,p).

Of course, one could try further optimising this geometry using DFT, however, is it really worthy? You have to consider that the system I am studying is a susbtrate within the active site of an enzyme. The initial structure was obtained by docking. Now I am trying to check whether or not the effect of a particular nearby residue on the electron density of the product of the enzymatic reaction would be sufficient to explain certain distortions observed in the EPR spectrum. So this is a semi-quantitative calculation.

This is the input I am using right now in order to compute the properties:

$CONTRL RUNTYP=HESSIAN $END
$CONTRL SCFTYP=RHF $END
$CONTRL MAXIT=200 $END
$CONTRL ICHARG=-1 MULT=1 $END
$CONTRL MOLPLT=.T. PLTORB=.T. AIMPAC=.T. $END
$DFT DFTTYP=B3LYP $END
$BASIS GBASIS=N311 NGAUSS=6 $END
$BASIS NDFUNC=2 NPFUNC=2 $END
$BASIS DIFFSP=.TRUE. DIFFS=.TRUE. $END
$SYSTEM TIMLIM=99999999999 MEMORY=268435456 $END
$SCF DIRSCF=.T. FDIFF=.T. $END
$ELPOT IEPOT=1 WHERE=PDC $END
$PDC PTSEL=GEODESIC $END

As you can see, this means DFT/6-311G++(2d,2p), I am trying to compute both AIM and ESP and, assuming that Mulliken and Lowdin will also be reported, I will then have a full set of data to compare.

Obviously, this far I am working only with the closed-shell species and not with the free radical reported in my first message. If this is successful, I will apply the same methodology to the free radical.

Kind regards,

Miro


On Sat Jan 17 '09 3:52am, Thomas Patko wrote
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>You may want to consider something like this:

>If you are having geometry optimization problems and are using DFT using GAMESS-US, the new DLC GDIIS geometry optimization engine in Firefly is quite fast and scales quite well (you will need version 7.1.D or newer for best results).  It should not be difficult to convert your GAMESS-US input file to the well optimized Firefly input file for such a Firefly geometry optimization run.  If you send over your GAMESS-US input options I can make some recommendations.

>The cost to enable the NBO option in Firefly is $30 only (very affordable) and you do not need to compile anything (just enter the license number and code in your input file).

>Just my 2 cents.

>Cheers,

>Thomas