Dear all,
I find an obvious bandgap underestimation in hBN monolayer by G0W0 in Yambo, as shown in the following figure.
After many testes with same parameters, the G0W0 gap at K point is calculated to be 7.40 eV, which is 0.37 eV smaller than that (7.77 eV) from BerkelyGW code in Table SI in Ref. (Phys. Rev. Lett. 128, 047402)(https://journals.aps.org/prl/abstract/1 ... 128.047402)
Another problem is that small QP gap at K will lead to small optical gap from BSE calculations, as shown in Table SII in Ref. (Phys. Rev. Lett. 128, 047402). The first exciton energy is calculated to be 5.45.5 eV, obviously smaller than experimental results (5.96.0 eV).
So, my question how to improve my calculations to get correct QP gap and exciton energy consistent with experimental results in BN monolayer?
Thanks a lot.
bandgap underestimation in hBN monolayer by G0W0 in Yambo?
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bandgap underestimation in hBN monolayer by G0W0 in Yambo?
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Dr. Yimin Ding
Soochow University, China.
Soochow University, China.
 palful
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 Location: Modena and Milan
Re: bandgap underestimation in hBN monolayer by G0W0 in Yambo?
Dear Dean,
Yeah, it is not easy to obtain results exactly on top of experiments, especially for large band gap materials.
First of all, let me point out that in the table SI of the reference you cite, they get a similar result to yambo (7.40 eV) when they use the fullfrequency approach for the dynamical screening, which is a more exact treatment (integrating explicitly over the frequency range) than the plasmonpole approximation (PPA) employed to get the larger value of 7.77 eV.
I assume that you are using the plasmon pole approximation in Yambo: the reason why the two PPAs give different result may be that the codes implement two different schemes: HybertsenLouie PPA for BerkeleyGW and GodbyNeeds PPA for Yambo. In a different system, it has been shown that HLPPA may tend to overestimate results [Phys. Rev. B 84, 241201(R), 2011].
Second: when you talk about agreement with experiment, consider also that in monolayer hBN the gap renormalization effects due to electronphonon interactions are very strong (reduction of ~0.5 eV). Considering that the luminescence emission peak is at ~6 eV and the (static) exciton binding energy is ~2 eV, we may estimate the "true" quasiparticle band gap only due to electronic correlations to be above 8 and below 8.5 eV. In the table SI, this is achieved only by the eigenvalueselfconsistent G0W0 approach of their Ref. [34], obtained with the code GPAW.
My suggestion, if you want to obtain reasonable results including the cancellation effects due to electronphonon corrections that you are not explicitly computing, would be to try an eigenvalueselfconsistent G0W0 calculation in Yambo using the GNPPA (or full frequency).
Cheers,
Fulvio
Yeah, it is not easy to obtain results exactly on top of experiments, especially for large band gap materials.
First of all, let me point out that in the table SI of the reference you cite, they get a similar result to yambo (7.40 eV) when they use the fullfrequency approach for the dynamical screening, which is a more exact treatment (integrating explicitly over the frequency range) than the plasmonpole approximation (PPA) employed to get the larger value of 7.77 eV.
I assume that you are using the plasmon pole approximation in Yambo: the reason why the two PPAs give different result may be that the codes implement two different schemes: HybertsenLouie PPA for BerkeleyGW and GodbyNeeds PPA for Yambo. In a different system, it has been shown that HLPPA may tend to overestimate results [Phys. Rev. B 84, 241201(R), 2011].
Second: when you talk about agreement with experiment, consider also that in monolayer hBN the gap renormalization effects due to electronphonon interactions are very strong (reduction of ~0.5 eV). Considering that the luminescence emission peak is at ~6 eV and the (static) exciton binding energy is ~2 eV, we may estimate the "true" quasiparticle band gap only due to electronic correlations to be above 8 and below 8.5 eV. In the table SI, this is achieved only by the eigenvalueselfconsistent G0W0 approach of their Ref. [34], obtained with the code GPAW.
My suggestion, if you want to obtain reasonable results including the cancellation effects due to electronphonon corrections that you are not explicitly computing, would be to try an eigenvalueselfconsistent G0W0 calculation in Yambo using the GNPPA (or full frequency).
Cheers,
Fulvio
Dr. Fulvio Paleari
S3CNR Institute of Nanoscience and MaX Center
Modena, Italy
S3CNR Institute of Nanoscience and MaX Center
Modena, Italy

 Posts: 106
 Joined: Thu Oct 10, 2019 7:03 am
Re: bandgap underestimation in hBN monolayer by G0W0 in Yambo?
Dear palfyl,
Thanks for yiur reoly.
1.As you said, "electronphonon interactions are very strong (reduction of ~0.5 eV).", is there any reference?
2. I have perform some limited eigenvalueselfconsistent GW calculations, which will increase QP gap by 0.30.4 eV. Then QP gap at K is still smaller than 88.5 eV.
3.Is there any tutorial using the full frequency in Yambo?
Thanks in advance.
Thanks for yiur reoly.
1.As you said, "electronphonon interactions are very strong (reduction of ~0.5 eV).", is there any reference?
2. I have perform some limited eigenvalueselfconsistent GW calculations, which will increase QP gap by 0.30.4 eV. Then QP gap at K is still smaller than 88.5 eV.
3.Is there any tutorial using the full frequency in Yambo?
Thanks in advance.
Dr. Yimin Ding
Soochow University, China.
Soochow University, China.