you can try:
1)Increase fshift in $scf to 0.15 or 0.20
2) Use larger maxdii in $scf e.g. maxdii=20 or 30
3) Use mom-default value of diimod in $scf. Valid values are 0 to 5, the default is 0.
See the recently updated manual for up to date description of $SCF group.
On Sat Nov 23 '13 6:36pm, Alex Nest wrote
>We have optimized a heme with 2 coordinational amino acids (above and under the heme plane), it is a big chromophore molecule with a Fe atom in the center and containing more than 100 atoms. The heme in high-spin reduced state was used for calculations. We used LANL2-DZ external basis-ecp combination, d5 was turned on, maxit,icut,itol and inttype was set up to improove convergency. In the SCF group following parameters was set:
> fdiff=.f. diis=.t. soscf=.f. dirscf=.t. damp=.t. shift=.t. nconv=6
>All this settings allows us to procceed geometry optimization in delocolized coordinates as well. Every step takes about 40-70 iterations of SCF for convergency. But in some conformations convergency takes more than 200 steps and the question is how to improve with Firefly abilities.
>In GAMESS-US (december 2011) convergency appears to be slightly better. May be because of step-by-step procedures: pure UHF -> UDFT in coarse grid -> UDFT in fine grid. I didn't find this ability in Firefly. May be firefly have some alternative techniques to improve the convergency in our case?
>DLC coordinates for optimization works in Firefly better than in GAMESS-US so we tend to use Firefly-only for energy minimization if UDFT-convergency can be improoved.