LCHIMAG with slightly doped semiconducting/metallic systems

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meb444
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LCHIMAG with slightly doped semiconducting/metallic systems

#1 Post by meb444 » Wed Nov 22, 2023 6:29 pm

Hi,

I am wanting to use the LCHIMAG method to simulate NMR spectra for lightly doped SrTiO3 systems. I was curious about the note that the method is only implemented for insulating systems, and that "The chemical shifts are calculated from the orbital magnetic response under the assumption that the system is an insulator. It makes no sense to use smearing schemes intended for metals, indeed, doing so can generate nonsense."

Is it still the case that no matter how slight the occupation of the conduction band is that the output will not be valid?

And if this is the case, why does running a calculation where there is slight occupation of the conduction band not result in a warning or error?

I attached an example of this below.
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fabien_tran1
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Re: LCHIMAG with slightly doped semiconducting/metallic systems

#2 Post by fabien_tran1 » Thu Nov 23, 2023 12:52 pm

Hi,

Indeed, the NMR implementation in VASP can not be used for metals (the Knight shift should also be considered). It is not clear to us if the results are reasonable or not when the occupation of the conduction band is small, and we should ask the specialists who implemented NMR in VASP. Actually, have you tried to obtain an empty conduction band by reducing SIGMA? If the band occupation with the value that you used (SIGMA=0.1) is tiny, maybe reducing SIGMA would finally lead to a real nonmetallic system.

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Re: LCHIMAG with slightly doped semiconducting/metallic systems

#3 Post by meb444 » Thu Nov 23, 2023 4:21 pm

Hi Fabien,

Thanks for the suggestion! I will test smaller sigma values and see if that can stabilize the system with an empty conduction band.

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