# How to perform charge analysis for a molecule

I am doing dehydrogenation of a molecule (say $$\ce{C12H12}$$) and I want to do charge analysis for dehydrogenated system ($$\ce{C6H6}$$). How I can proceed? I can use Quantum ESPRESSO and Gaussian codes. Also, I would be grateful, if you can advice me the physical significance of the charge analysis of a molecule.

• Jan 10, 2021 at 20:27
• +1 but please see the edit I made and keep it in mind for next time. Also, we have chat rooms for both Quantum ESPRESSO: chat.stackexchange.com/rooms/117642/quantum-espresso and GAUSSIAN: chat.stackexchange.com/rooms/110569/gaussian, can you please enter both rooms and say at least "hello" so we're aware of your interest in these programs? Thanks again for all our contributions to our community! Jan 10, 2021 at 21:08
• pop=mk in gaussian will produce Merz-Kollman ESP fitted charges, which is an often used scheme. Jan 11, 2021 at 17:59
• I am sorry for the late response. My aim is to study like bond order and natural population analysis. I do not want to use gaussian as for my catalysist+molecule, it may fail. So I would prefer for a DFT code (Quantum Espresso is my first choice) Jan 16, 2021 at 19:32

This is a very general answer, but let me point you in the right direction at least. If you are looking at a molecular system such as C6H6, you will likely want to use a non-periodic code such as Gaussian. This page describes many different methods of charge analysis and you can use this information to calculate charge transfer complexes and local charges on individual atoms.

You should read the literature of your specific field for what method of charge analysis is best, but that will require more information.

• I am sorry for the late response. My aim is to study like bond order and natural population analysis. I do not want to use gaussian as for my catalysist+molecule, it may fail. So I would prefer for a DFT code (Quantum Espresso is my first choice) Jan 16, 2021 at 19:31
• @astha Gaussian is a DFT code and in fact, you will struggle to do bond order / natural population analysis in a planewave based code more so than Gaussian. Jan 16, 2021 at 19:49
• I just want to avoid gaussian due to license issue. Jan 16, 2021 at 19:50
• @astha See similar codes such as Orca then. You want a Gaussian-like code, not a Quantum Espresso-like code. Jan 16, 2021 at 19:51

Complementing the answer by @Tristan, in this question you will find the several methods used to determine the atomic charges.

Also, you can use Gaussian to calculate/export the wavefunction and them use Multiwfn package to estimate the system charges using several approaches:

• Population analysis. Hirshfeld, Hirshfeld-I, VDD, Mulliken, Löwdin, Modified Mulliken (including three methods: SCPA, Stout & Politzer, Bickelhaupt), Becke, ADCH (Atomic dipole moment corrected Hirshfeld), CM5, CHELPG, Merz-Kollmann, RESP (Restrained ElectroStatic Potential), RESP2, AIM (Atoms-In-Molecules), EEM (Electronegativity Equalization Method) and PEOE (Gasteiger) are supported. Electrostatic interaction energy of two given fragments can be calculated based on atomic charges.
• Orbital composition analysis. Mulliken, Stout & Politzer, SCPA, Hirshfeld, Hirshfeld-I, Becke, natural atomic orbital (NAO) and AIM methods are supported to obtain orbital composition. Orbital delocalization index (ODI) can be outputted to quantify extent of spatial delocalization of orbitals.
• @astha See my comment above Jan 16, 2021 at 19:49