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

[ma...@gmail.com]

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
>>
>
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