QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: skg on May 8, 2014, 12:55

Title: Charge transfer from the charge density
Post by: skg on May 8, 2014, 12:55

Hi,
please explain. can we calculate charge transfer from material to adsorbed atom in atk.




thanks

Title: Re: Charge transfer from the charge density
Post by: zh on May 9, 2014, 02:26

You may calculate the charge density difference to discuss the charge transfer:
\delta \rho = \rho(adsorbate+substrate) - \rho (adsorbate) - \rho (substrate)

For the more detailed explanation on the above formula, you may refer to the following webpages:
http://www.tcm.phy.cam.ac.uk/castep/documentation/WebHelp/extfile/castep_tuts/html/castep_dens_diff_tut.htm
http://vaspnotes.blogspot.jp/2013/10/charge-density-difference-plots.html

The steps listed in the above two webpages can be done similarly in the ATK code.

Title: Re: Charge transfer from the charge density
Post by: Anders Blom on May 9, 2014, 06:05

Another simpler but also more approximate way to estimate the charge transfer is to look at the Mulliken population of the atom in the composite configuration. It's only good enough for a first approximation, but can give some hint at least if the charge transfer is positive or negative, and if it's large or small.

Title: Re: Charge transfer from the charge density
Post by: GJK on May 26, 2014, 19:55

Dear Mr.Anders,

Could you please explain how to gea rough idea of charge density from Mulliken population???

Because it has many orbitals values etc.

Thanks

Title: Re: Charge transfer from the charge density
Post by: Anders Blom on May 26, 2014, 21:25

Orbital values are just the decomposition. Each atom has a Mulliken population which is a single number per atom, and can be compared to the valence charge. For instance C with the normal pseudopotentials has valence charge 4 (sp3). If your Mulliken population is 4.2, then 0.2 electrons have been transferred to this atom.

Title: Re: Charge transfer from the charge density
Post by: GJK on May 27, 2014, 10:24

Quote from: Anders Blom on May 26, 2014, 21:25

Orbital values are just the decomposition. Each atom has a Mulliken population which is a single number per atom, and can be compared to the valence charge. For instance C with the normal pseudopotentials has valence charge 4 (sp3). If your Mulliken population is 4.2, then 0.2 electrons have been transferred to this atom.

Thanks.But I have a doubt.The example which you quoted....Carbon with Mulliken population 4.2...The Charge transfer is positive or negative???

Already in the earlier post you have given the link to calculate charge difference density Δρ = ρAB - ρA-ρB.
If Δρ is positive --what it means???
If Δρ is negative --what it means???

Title: Re: Charge transfer from the charge density
Post by: Anders Blom on May 27, 2014, 11:07

4.2 means 4.2 electrons on the atom. The rest should be obvious from that.

Title: Re: Charge transfer from the charge density
Post by: GJK on May 27, 2014, 12:28

Dear Mr.Anders,

You mean
if the atom has gained electrons(eg: carbon 4-4.2 in Mulliken population) -positive charge transfer
if the atom looses electron (eg: carbon 4-3.8 in Mulliken population)-negative charge transfer

I am telling these with respect to the valenec electrons of an atom as you suggested.

Am I right???