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

[Nicholas Winner]

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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