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sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,773

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RESP charge by ORCA output

Today I find a question in ResearchGate (https://www.researchgate.net/post/RESP_ … RCA_output), which is related to Multiwfn, below is the question and my reply. I copy them here since other uses may have interesting in this topic

Q:RESP charge by ORCA output

I am trying to get the RESP charges from ORCA calculations in a way similar than in the antechamber, but I am not finding any software that is able to do the fitting in the ORCA outputs. I have tried Multiwfn but the options are CHELPG, AIM, MK and HI.

My problem with the Multiwfn is the lack of equivalence on the atoms charges. I am using a dimer to get the charges, but one of the molecules is symmetrical and when I get the charges by CHELPG in Multiwfn there isn't a equivalence on the atoms. The atoms with the same atom type have different charges.Is there a way to restrain or constraint the charges to force all the atoms with the same atom type have the same atomic charge?

Does anyone know how to procedure?

A:

Fortunately, calculation of RESP charge has been *perfectly* supported by Multiwfn in its latest version. Please go to//www.umsyar.com/multiwfnto download the latest version (the current latest version is the 3.6(dev) updated on 2018-Sep-12), and follow the examples given in Section 4.7.7 of the latest version of manual. Multiwfn makes calculation of RESP charge extemely easy. The .molden file outputted by ORCA can be directly used as input file. The RESP module of Multiwfn can not only calculate standard RESP charges, but can also calculate normal ESP fitting charges with customized penalty function, equivalence constraints, charge constraints and multi-conformation consideration.

The underlying reason that spatially equivalent atoms do not have equivalent charges is that the fitting points of CHELPG method are not distributed in accordance with molecular symmetry. If you do not intend to use the new RESP module of Multiwfn to manually impose equivalent constraint on that atoms, you can try to change the CHELPG method to MK method (subfunction 13 of main function 7), if the symmetry of atomic charges is still not satisifed well, you can then try to increase the density of fitting points (there are options used to set parameters of fitting points in the MK and CHELPG interfaces), this problem should be alleviated.