[CP2K-user] Incorrect spin moment for P donor in Si

[ma...@gmail.com]

Dear Nick,

These information are very helpful! Thank you very much!

Regards,
Hongyang

在2021年4月22日星期四 UTC+10 上午4:05:09<n... at berkeley.edu> 写道：

>
> HSE should give alright levels for P in Si. I have a test calculation I 
> did a while ago with Si:P and found the following:
>
> Dopant energy levels (distance from band edge) for Boron, Phosphorus 
> Exp:      0.045eV, 0.045eV
> PBE0:   0.21eV, 0.28eV
> HSE06: 0.12eV 0.19eV
>
> While by experimental standards those energy levels are pretty far off, 
> it's pretty darn good by DFT with total energies. 
>
> Using Janak's theorem instead of total energies for the transition levels:
> PBE0:   0.104 eV, 0.176eV
> HSE06: 0.017 eV, 0.077eV
>
> Which is even better. HSE will help give pretty good localization, so that 
> might not be the issue you are facing. You should try some delocalization 
> analysis to see if its actually the problem. You can do this with, say, the 
> planar averaged electrostatic correction scheme of Freysoldt. You can also 
> look at the localization by investigating the cube file for the electron 
> density in a program like vesta. The hyperfine constant may require even 
> better theory like a GW calculation, but I'm not an expert on that aspect 
> of point defect calculations.
> On Monday, April 19, 2021 at 10:37:47 PM UTC-7 ma... at gmail.com wrote:
>
>> Hi Nick,
>>
>> Thank you for your response. Yes, P is a very shallow donor. I calculated 
>> this system using VASP at first but it couldn't give good hyperfine 
>> constant either which I thought maybe due to the delocalization of 
>> pesudopotential used in VASP. So I tried cp2k because I though Gassusian 
>> type basis set maybe more localized. I tried HSE too but it couldn't give 
>> good results either. Could you please provide some suggestions on improving 
>> this issue?
>>
>> Regards,
>> Hongyang
>>
>> 在2021年4月20日星期二 UTC+10 上午3:31:14<n... at berkeley.edu> 写道：
>>
>>> The main thing is because you are trying to simulate a shallow donor 
>>> with GGA. If you look at The HOMO-LUMO gap in your output file, one of the 
>>> spin channels has a gap of 0.6eV, which is the expected band gap of Si 
>>> using GGA approximation. The other spin channel, where the extra P electron 
>>> has gone, however, has a negative HOMO-LUMO gap. This is because the P 
>>> state has delocalized into the conduction band rather than remaining in the 
>>> gap. DFT with GGA will have issues of delocalizing defect states, and they 
>>> will become more and more pronounced the shallower that defect state is, 
>>> since the defect state will couple to the band edge. P is an extremely 
>>> shallow state in Si (~0.045eV below the CB in experiment), and so it's very 
>>> hard to remedy this situation. Your best bet is to explore hybrid DFT, 
>>> which opens the band gap and provides more localized states, but even that 
>>> will have trouble for such a shallow state and so you'll have to check it 
>>> as you go.
>>>
>>> -Nick
>>> On Sunday, April 18, 2021 at 11:23:23 PM UTC-7 ma... at gmail.com wrote:
>>>
>>>> Dear cp2k developers/users,
>>>>
>>>> I'm curretly using cp2k 7.1 to calculate the P doped Si system (1P in 
>>>> 512 atoms). Theoretically, since the electronic configuration of P is s2p3 
>>>> and that of Si is s2p2. A P doping in Si should result in a total spin of 1 
>>>> due to the unpaired electron introduced by the P atom. 
>>>> In my calculation, the number of total spin is correct, but the spin 
>>>> moment of each atoms seems to be wrong because the spin moment of P should 
>>>> be 1 (because of the unpaired electron in P) and that of Si should be 0. 
>>>> Could someone please provide some help in solving this issue? Thanks.
>>>>
>>>> Thanks & Regards,
>>>> Hongyang
>>>>
>>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20210421/9c3b0056/attachment.htm>