[QE-users] hp.x - appropriate way to handle single dopant

[Abdul Muhaymin]

Dear Dr. HOUARI,

Thank you for your reply. I did not correct the band gap in any system. 
I am hoping if I apply some U parameter to Zn-3d, Co-3d and maybe to 
S-3p, I can capture the physics better. In this pursuit, some V 
parameter might also be an option. But this is not the problem I am 
facing. I am facing problem on how to obtain these U and V values. For 
undoped, periodic system, we can get the value using hp.x with simple 
unit cell. But the problem is for aperiodic doped system like the one I 
have.

As you said, the calculated U from the 8 atoms ZnS unit cell is probably 
okay to use for 64 atoms supercell. But if I dope the unit cell (to get 
the U value of Co), this system (25% doping) is much different than the 
64 atoms supercell (3.125% doping). And when I am trying to run hp.x 
directly for the 64 atoms (U applied only to the single Co), only a 
single iteration of 1 q point takes an hour using 2240 CPUs. So, it 
would take weeks to complete a calculation!

I am hoping maybe I can calculate the U parameter separately for Co unit 
cell (i.e., Co-HCP) and then maybe for Zn and S from ZnS unit cell. But 
I have no rationale to support that it should work. And also the 
inter-site parameters cannot be obtained following this.

Sincerely,
Abdul

On 5/21/2024 7:03 PM, Abdesalem Houari wrote:
> Dear Abdul Muhaymen,
>
> You say that your results are fine, except the band gap ! How did you 
> correct it in pure ZnS, before Co-doping ?
> The most commun way in DFT is hybrid functionals (like HSE 06), which 
> obviously are very demanding in computational cost. So the DFT+U (+V) 
> could be a nice alternative. Here I think you might need on-site U not 
> only for Co, but also for Zn (and as you said may be S). Since ZnS is 
> a band insulator and covalent compound, the inter-site V could play an 
> important role.
>
> In principle U and V parameters are neither transferable nor 
> universal, but in your case ( calculated U from 8 atoms unit cell to 
> use in 64 atoms supercell), Iguess it should be OK !
>
> Best regards
>
>
>
> =====================================
> Dr. Abdesalem HOUARI
> -------------------------------------------------------------------------------------------
> Department of physics, Theoretical Physics Laboratory
> University of Bejaia-06000. Algeria.
> E-mail: abdeslam.houari at univ-bejaia.dz & habdslam at yahoo.fr
> https://sites.google.com/site/houariabdeslam/homepage
> ===================================
>
>
> On Tuesday, 21 May 2024 at 04:17:30 am GMT+1, Abdul Muhaymin via users 
> <users at lists.quantum-espresso.org> wrote:
>
>
> Hello all,
>
> I am investigating single TM dopant in wide band gap semiconductors such
> as Co in ZnS. I am using a 64 atoms supercell where I replaced one of
> the Zn atom with a Co atom. I tested several convergence with respect to
> the supercell size. My results seem fine except the band gap. Now I want
> to apply the U correction to that Co-3d (and maybe to S-2p). For this,
> is it possible to use the unit cell (8 atoms) and run hp.x to get the U
> values? Or do I have to run hp.x with the large supercell (2*2*2 unit
> cell=64 atoms)?
>
> Also, at the beginning of our studies, during the structural relaxation
> phase, we first found our lattice parameter for the host semiconductor
> from multiple scf calculations and subsequently running an eos analysis
> (ev.x). Then we ran relax calculation but not vc-relax. We keep this
> lattice parameter constant and when introducing new dopants, we only
> vary the atomic positions (calculation='relax'). In this case, when
> running hp.x, could we replace the vc-relax calculation with relax
> calculation to self-consistently get the U values?
>
> Thanks,
> Abdul Muhaymin
> Graduate (MS) student, Materials Science and Nanotechnology
> Bilkent University, Ankara.
>
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