Multiwfn forum / RESP charge fitting on Fe-S cluster

Re: RESP charge fitting on Fe-S cluster

dummy@example.com (sobereva) — Thu, 22 Jul 2021 10:46:29 +0000

Negative charge of transition metal doesn't necessarily imply the result is incorrect. S do not have large electronegativity and Fe do not have small electronegativity. In addition, it should be noted that RESP charges focus on reproducing ESP distribution in the region close to vdW surface rather than exhibiting atomic intrinsic charging statuses, the former is more important for representing electrostatic interaction in forcefield calculation.

RESP charge fitting on Fe-S cluster

dummy@example.com (saurav01) — Thu, 22 Jul 2021 08:35:46 +0000

Hi there,

I tried to fit MK charges (calculated from Gaussian) to some 4Fe4S cluster compounds but I observe negative charges being assigned to iron ions. This seems to be illogical from theory. I tried to apply constraints (in many possible ways) but could not stop Multiwfn assigning Fe ions to have negative charge. I needed RESP charges for ONIOM calculations. Is there anyway I can get logical RESP charges for Fe ions in cubane compounds? Please let me know.
Thanks.

-Saurav P.