Hi.
If your calculation GW+BSE are well converged, probably your results are not
wrong at all: if your BSE optical gap is in agreement with the experimental
one, it can be related with some cancellation between the opening of the
electronic gap by the GW correction and its following reduction due to
excitonic effects when calculating the excitonic contribution.
What about the optical experimental gap thou?
I do not know if y our input file is the one to prepare the yambo run or not.
In this case, I think the run should be with QE a NSCF calculation with large
number of empty band and different mesh of increasing k point in order to check
the convergence for the screening calculation (GW part) and the BSE part
afterwards.
Did you converged correclty the W screening even wr.t. the G vector ?
Remeber the BSE converges with few bands but usually it requires more k point
than the GW part.
HTH.
Federico
Federico IORI
Marie Curie Fellow
Laboratoire de Physique des Solides
Bâtiment 510 - Rue André Rivière
91400 Orsay
----- Mensaje original -----
De: "Christoph Wolf(신소재공학과)" <[email protected]>
Para: "pw forum" <[email protected]>
Enviados: Jueves, 8 de Septiembre 2016 4:11:49
Asunto: Re: [Pw_forum] Convergence or band-gap problem in orthorhombic CsPbBr3
Dear Frederico!
The experimental band gap is 2.3-2.4 depending on the method used; my band gap
is less than 0.5 eV – rather drastic underestimation. For the orthorhombic
phase there are two or three references, but they do not agree well in terms of
the location of the gap (sometimes gamma, sometimes R-point) and I am not sure
if they applied scissors (it is not stated in the manuscript).
The interesting thing is that the BSE absorption spectrum for the cubic cspbbr3
(a=5.6 A) agrees quite well with my experimental values but the XRD pattern
suggests I have o-CsPbBr3. I am following the YAMBO GaSb tutorial (it
calculates exactly what I want to calculate); but I am curios where I went
wrong with my scf/nscf calculation…
Thank you for your suggestions!
Yours,
Chris
Christoph Wolf
POSTECH university
Dep. Materials Science and Engineering
Chung-am ro 77
Pohang, Gyungbuk
Republic of Korea
30POSTECH
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