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Miro Moman
edelmiro.moman@gmail.com

I am trying to optimize the geometry of a [Fe4S4]+ cluster.

In fact, the entire structure is [(Fe4S4)(C2H2)(SCH3)3]-2.

Having had problems with the full complex, I am now focusing on [Fe4S4]+

This is my current input file:

$CONTRL SCFTYP=UHF MULT=2 MAXIT=200 dfttyp=pbe0 d5=1 icharg=1 $END
!$CONTRL RUNTYP=OPTIMIZE $END
$CONTRL INTTYP=HONDO $END
$SYSTEM TIMLIM=99999 MWORDS=99 $END
$SCF DIIS=.T. $END
$statpt nstep=1000 $end
$scf dirscf=.t. fdiff=.f. $end
$guess guess=moread norb=376 $end
$smp httfix=.f. smppar=.t. $end

I have tried many different options in a more or less combinatorial way, such as : ICUT=11, ITOL=30, rstrct=.t., fdiff=.t., etc.

I have tried with larger and smaller basis sets (currently Def2-TZVP) and also I have used HF instead of DFT. In addition, thinking that the initial geometry could be the culprit, I have tried to optimize it.

Often it seems that the density has nearly converged, but it oscillates quite a lot, for instance:

 90 89 -6646.252407632     0.000030038   0.012915252   0.000146340     1661471091   9105267
 91 90 -6646.252436008    -0.000028377   0.004901678   0.000065611     1661477904   9105225
 92 91 -6646.252446605    -0.000010597   0.001334835   0.000051306     1661481388   9105176
 93 92 -6646.252449524    -0.000002919   0.002216061   0.000043654     1661486660   9105169
 94 93 -6646.252454263    -0.000004739   0.000922602   0.000045303     1661496334   9105149
 95 94 -6646.252456240    -0.000001977   0.002316391   0.000044423     1661501828   9105141
 96 95 -6646.252461196    -0.000004956   0.001103882   0.000043711     1661505726   9105136
 97 96 -6646.252463602    -0.000002406   0.000039273   0.000042713     1661508744   9105140
 98 97 -6646.252463639    -0.000000037   0.000755261   0.000041815     1661508666   9105145
 99 98 -6646.252462045     0.000001594   0.000914736   0.000042353     1661506603   9105146
100 99 -6646.252463837    -0.000001792   0.004938129   0.000042491     1661508480   9105138

Any suggestions?