About changing charge/multiplicity during QM-MM

From: Francesco Pietra (chiendarret_at_gmail.com)
Date: Mon Mar 25 2019 - 02:16:35 CDT

I dare posing a general question on QM-MM, surely a naive question to those
experienced with QM-MM (I am doing such simulations for the first time).

I am observing a change in my metalloprotein system where apparently the
iron ions become bounded to other ligands, changing from FeII to FeIII. The
overall charge/multiplicity is not maintained, as far as I can understand.
Nonetheless, ORCA is repeating its SCF cycles, converging after a number of
cycles. I have already restarted the simulation six times for 24hr on 36
cores with the same settings, in particular as to the charge and
multiplicity, and the structure of the complex is no more changing, as far
as it can be judged from geometry. I can't figure out how the system
readjusts itself so that the QM calculation can go on.
Thanks for any comment
francesco pietra

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