Poor convergence using Fe HMOs for FMO in Gamess

[WillCawdell]

Hello!

I'm trying to model an interaction between ligands and a heme group using FMO in Gamess.

I've tried to make HMOs for the FMOBND section of the input file (using an Fe-F complex), the HMOs are shown below:
STO-3G 19 5
0 1 0.992624, 0.019366, 0.000000, 0.000000,-0.000001,-0.014838, 0.000000,
0.000000, 0.000004, 0.005535, 0.005534, 0.005534, 0.000000, 0.000000,
0.000000,-0.000595, 0.000000, 0.000000,-0.000029
1 0 0.420492,-1.033033, 0.000000, 0.000000,-0.000111,-0.314157, 0.000000,
0.000000, 0.000062, 0.110327, 0.111004, 0.109981,-0.000339, 0.000000,
0.000000,-0.010802, 0.000000, 0.000000,-0.000514
0 1 -0.000040, 0.000094, 0.000000, 0.000000,-0.990859, 0.000170, 0.000000,
0.000000,-0.026700,-0.000085,-0.000086,-0.000094, 0.000001, 0.000000,
0.000000, 0.000139, 0.000000, 0.000000, 0.002284
0 1 0.000000, 0.000000, 0.928325, 0.346200, 0.000000, 0.000000, 0.025225,
0.009407, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000008,
0.000003, 0.000000,-0.001955,-0.000729, 0.000000
0 1 0.000000, 0.000000,-0.346473, 0.929057, 0.000000, 0.000000,-0.008635,
0.023155, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000,-0.000003,
0.000009, 0.000000, 0.000689,-0.001848, 0.000000

These HMOs work to a certain extent, allowing monomer calculations on the heme group, cysteine donor and my ligand donor to converge, however the value they converge to is oscillating between 2 points thus never converging according to Gamess. So the calculation cannot proceed to the dimer stage.

Does anyone have any ideas how to make my convergence better? U currently use DIIS as a start an initial convergence mode then switch to SOSCF to fine tune the convergence value

Thannks a lot in advance!

 

[jim mcnamara]

Calling @TeethWhitener - can you help?

Home link -
https://www.msg.chem.iastate.edu/gamess/

 

[TeethWhitener]

These HMOs work to a certain extent, allowing monomer calculations on the heme group, cysteine donor and my ligand donor to converge, however the value they converge to is oscillating between 2 points thus never converging according to Gamess. So the calculation cannot proceed to the dimer stage.

Does anyone have any ideas how to make my convergence better? U currently use DIIS as a start an initial convergence mode then switch to SOSCF to fine tune the convergence value

Caveat 1: I've never been great at solving SCF convergence problems, and I'm not sure anyone actually is. It's a bit of an art.
Caveat 2: I never really used GAMESS as extensively as some other QC programs, so I'm not as familiar with its syntax and its capabilities.

If your convergence value is oscillating between two points, it might be the case that the ground state and the first excited state are fairly close in energy, and the program can't decide which one is which. If you know which one is your ground state, and if its orbital occupation numbers are significantly different from the first excited state, you might be able to resolve the problem with a better initial guess. Absent that, you could try DIIS damping or turn off DIIS completely. This will take longer but might help convergence. Good luck.

 

[WillCawdell]

Caveat 1: I've never been great at solving SCF convergence problems, and I'm not sure anyone actually is. It's a bit of an art.
Caveat 2: I never really used GAMESS as extensively as some other QC programs, so I'm not as familiar with its syntax and its capabilities.

If your convergence value is oscillating between two points, it might be the case that the ground state and the first excited state are fairly close in energy, and the program can't decide which one is which. If you know which one is your ground state, and if its orbital occupation numbers are significantly different from the first excited state, you might be able to resolve the problem with a better initial guess. Absent that, you could try DIIS damping or turn off DIIS completely. This will take longer but might help convergence. Good luck.

Thanks a lot for your help! I agree convergence is a black art! I appreciate what you're saying about the ground and excited states I should have thought of that sooner! I think I'll try the DIIS changes you suggested! Thanks!

 

[TeethWhitener]

I'll keep my fingers crossed for you. If that doesn't work, it's not a bad idea to poke around google or some of the QC program forums for advice on convergence problems.