SCF convergence failure


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Hello,

I have SCF convergence failure problem. The system has about 180 atoms (12 Fe atoms) and the iterations is 800 for my first trial. After 800 SCF cycles the output showed "Calculation failed to converge" and then stopped. I know sometimes the initial structure will affect SCF convergence. I also tried:

Convergence lshift 0.5

and:

Convergence damp 70

I don't want to change the criteria of energy threshold. Increase maxcyc may be helpful (I tried at most 2,000 iterations) Does anyone have better suggestion for SCF convergence?

Thanks,
Chun-Hung