Dear Zsolt,
ccmaxit sets the maximum number of iterations for ccsd executable containing the faster CCSD code.
If you, for some reason, need to increase the number of iterations for the mrcc executable containing the general order CC codes, you can change the maxit variable in the MRCCCOMMON file and recompile the complete codebase.
However, your problem is probable originated in the SCF step as your UHF calculation is not converged and appears to be wrong. So you should fix that first and then the CCSD iteration has a much better chance to converge.
Additionally, there are a couple of keywords in your input that deviate from the defaults and you should check carefully whether those are needed/helpful:
dft=user # this is unnecessary
0
ccprog=mrcc # for CCSD only ccprog=ccsd is recommened, ccmaxit works with that
scfiguess=ao # this is gernerally not the best guess choice
core=corr # this will correlate all electrons, including 1s, 2s, 2p on Fe and 1s on O, basis set is unsuitable for that
Best wishes,
Peter
