Multiwfn forum

brunosamp

Member

Registered: 2023-04-21

Posts: 18

Charge density difference analysis for graphene

I am studying the PDOS (Partial Density of States) of a graphene oxide structure, with only hydroxyl groups.
To study the PDOS, it's useful to evaluate the charge transfer from the carbon to the OH functional group.
I understood how to perform the charge density difference map in a excitation process. But in my case, i just want to evaluate how the electron density is distributed towards that OH group.
1) Can i obtain the isosurface of charge density difference, in my case, using the method in 4.18.3 section.
2) Can i measure the amount of charge transfer (Q) from the carbon to the OH group using Multiwfn? I couldn't find something about this in the manual.

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,833

Website

Re: Charge density difference analysis for graphene

1 Please check Section 4.5.5 of Multiwfn manual, there is an example of plotting density difference map between fragments.

2 Calculating fragment charge of OH group. Assume that it is -0.2, that means 0.2 electron is transferred from carbons to OH.
You can manually sum up atomic charges to obtain fragment charge. A more convenient way is using option -1 of main function 7 to define a fragment first, then, after calculating atomic charges as usual, fragment charge will be directly printed.

brunosamp

Member

Registered: 2023-04-21

Posts: 18

Re: Charge density difference analysis for graphene

Tian lu, thank you for your response! One question: for the second method, shouldn't i measure the charge in the carbon, in which the OH group is attached, without the OH group?
For example: without the OH group, the charge of the carbon is -0.02. But after attaching the OH group, this same carbon has 0.065 charge (i used the method you mention in "2" for both structures). So, wouldn't the charge transfer be 0.085, from the carbon to the OH group?

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,833

Website

Re: Charge density difference analysis for graphene

Introducting an OH group affect both electronic structure and geometry structure of graphene. It you take graphene in isolated electronic and geometry structure as reference, then atomic charge of all carbon atoms should be exactly zero, since all carbon atoms are in the exactly identical chemical environement. In this case you just need to calculate charge of OH group.

brunosamp

Member

Registered: 2023-04-21

Posts: 18

Re: Charge density difference analysis for graphene

Sir, now i understand it. Thank you very much!