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QuantumATK => General Questions and Answers => Topic started by: meena on August 21, 2017, 12:03

Title: Hubbard U
Post by: meena on August 21, 2017, 12:03

Dear staff

what is the hubbard U potential for carbon and fluorine atom


thanks

Title: Re: Hubbard U
Post by: berna on August 21, 2017, 12:13

I think you do not need Hubbard U correction for carbon and its allotropes. Because C atoms do not have d or f orbitals.

Title: Re: Hubbard U
Post by: meena on August 21, 2017, 12:55

hello

What about the hubbard U potential for fluorine

Title: Re: Hubbard U
Post by: berna on August 21, 2017, 13:07

Atomic number of fluorine is 9. Its orbital configuration is 1s2 2s2 2p5. Then you don't need to use Hubbard term for fluorine, either.

Title: Re: Hubbard U
Post by: Anders Blom on September 8, 2017, 01:08

There is no such things as "the" U value for any element. You adjust the U values to change the band gap of certain materials, typically by fitting to experimental values. In general it helps people answering your questions if you provide a bit more information, such as "I need this because I'm trying to get a more correct band gap of material X, and I'm getting a too low value with LDA compared to papers I've read, e.g. PRB 123, 222xx (1995)".

Now, you don't strictly need the material to have d-orbitals to use a Hubbard model, but the theoretical background kind of assumes that the band gap changes due to an improved description of the localization of d-electrons.