Adding charge to specific element

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nimali_rathnayake
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Adding charge to specific element

#1 Post by nimali_rathnayake » Wed Jun 16, 2021 2:32 am

Hi,

I am working with sodium-diglyme system and I want to use Na with +1 charge. Can we specifically add charge to Na in VASP? I used NELECT tag. But, it will charge the whole system.

If we could use charge specific atom using VASP, Could you please explain to me how to do that?

Thank you.

Nimali

martin.schlipf
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Re: Adding charge to specific element

#2 Post by martin.schlipf » Wed Jun 16, 2021 6:48 am

Could you explain what you want to achieve? If you remove one electron from Na, the other electrons in the system will rearrange which is exactly what the NELECT tag does. I don't think that it is very appropriate to use a ground state method like DFT to study the initial state with the single Na electron removed before the relaxation.
One exception to this is core level spectroscopy, so you can look into that, if that is what you want to achieve.

nimali_rathnayake
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Re: Adding charge to specific element

#3 Post by nimali_rathnayake » Thu Jun 17, 2021 2:02 am

Hi,

Thank you for your reply. I am working on Na-diglyme system. In the real Na-diglyme complex Na has +1 charge. Therefore, I want to add +1 charge to Na. Otherwise my calculation is wrong. To get the correct results, I need to use Na-ion (+1 charge).

I would like to know how to do this in VASP.

Thank you.

martin.schlipf
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Re: Adding charge to specific element

#4 Post by martin.schlipf » Thu Jun 17, 2021 8:13 am

I think there may be an misunderstanding of oxidation states. When chemists say Na is in +1 oxidation state that is just a simplification based on a simple orbital picture. In reality a small fraction of orbital will still be close to Na and only most of it is around the anion. This is the default behavior of VASP if you don't set anything. Only when the whole molecule is charged like [Na(diglyme)2]+ you would start changing NELECT from its default.

Note that in either case the oxidation state of +1 is a result of the calculation, not something that you need to put in. If you calculate a molecule, you can use the LORBIT tag in VASP to determine the primary orbital character for each molecular orbital. Then you can see that when you simulate the system the Na 3s orbital is empty and one orbital of the anion is filled instead. Please verify this for yourself on a simple system like a NaCl molecule.

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