Multiwfn forum

CoinMcCoin

Member

Registered: 2019-02-27

Posts: 3

Transition Metal RESP charges??

Hi all again,

Just wanted to probe the expertise on this board, though its more of a theoretical issue rather than a software one. I have calculated the RESP charges using multiwfn for a small library of transition metal complexes (namely octahedral Ruthenium polypyridyls so coordination of 6 nitrogens) and I have stumbled across a potential mental hurdle. The complexes were optimised in Gaussian with a charge of +2 (singlet), this is due to the formal oxidation state of the metal centre being +2 (i.e. not charged ligands). The RESP charges however have all calculated the metal centers as having charges in the range of (-1.5<x<-1.2). Now i know formal charge is not perfect and the real charge distribution is rarely close to the formal, but to go from an expected +2 charge to -1.5???

My questions is: Is RESP charge calculations accurate for T.M's? and if so, is it normal to see such a deviation in atomic charge?

Any help would be most appreciated, thank you in advance.

Kane

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: Transition Metal RESP charges??

You can try to use CHELPG and MK, if the transition metal charge is still very negative, the reason should be that the ESP fitting method in principle doesn't work well for your systems. In transition metal complexes, the transition metal is often very heavily buried, in this case its fitted charge is numerically unstable (because the fitting center is very far from fitting points) and the result doesn't make great sense. In this case you should employ other kinds of atomic charges instead, such as ADCH, Hirshfeld-I, etc.

Tian