[QE-users] HOMO is higher than LUMO

[Mahmoud Payami Shabestari]

Dear Lorenzo,



Hello.

Thank you so much for your explanation.

I will follow your suggestions.



Bests,

Mahmoud









From: Lorenzo Paulatto <paulatz at gmail.com>
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Date: Sun, 21 Feb 2021 20:18:09 +0100
Subject: Re: [QE-users] HOMO is higher than LUMO


Hello,
this happens when the system is a bad metal, with a pocket of valence 
electrons in a small Fermi surface. I.e., at some point in the Brillouin 
zone, the n-th band is lower in energy than the (n-1)-th band somewhere 
else, but these two bands do not touch. Just use a smearing for occupation 
and you'll solve the issue. Do not forget to recheck k-points convergence in 
the new case.


regards


--
Lorenzo Paulatto - Paris
On Feb 21 2021, at 7:05 pm, Mahmoud Payami Shabestari <mpayami at aeoi.org.ir> 
wrote:
Dear QE-users/Developers,
 
In DFT+U calculation of an AFM pure system, I used an input file in which I 
had not used "occupation" card, but only a few bands more than half of the 
number of electrons. Then, the SCF run was successful, and in the output I 
get both HOMO and LUMO values correctly aligned, i.e., E_LUMO > E_HOMO.
However, when I add a metallic impurity (without changing the other 
parameters), the SCF run successfuly ends and in the output now I get E_HOMO 
> E_LUMO (!!).
I do not know how to interpret this result. Is there any miscalculation?
Any comments is highly appreciated.
 
Best regards,
Mahmoud Payami
AEOI, Tehran, Iran
 
Email: mpayami at aeoi.org.ir
Phone: +98 (0)21 82066504
 
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