The band gap and exciton spectrum of MgO

[qiaofen1]

Hi, all,
I’m a new user . Following the example LiF, I calculated the MgO. The KSS file is produced by abinit. The ngkpt is 11 11 11. The GW and BSE calculation were performed by Yambo. I meet two questions now.
1.Why the first peak of imaginary part of dielectric function of MgO in Fig1 and Fig.2 is so small, and is different from that E peak in the Fig.3 by schleife ?
2.In Fig.2, The Eg-LDA=4.656 eV, EQP=2.160 eV, so the Eg-gw= 6.816 eV;
Why is the GW band gap calculated using Yambo for MgO about 1 eV smaller than the experimental value (7.8 eV) ?
(The experimental band gap is 7.8 eV, so besides the QP correction, I also use the scissor correction, about 0.98 eV when I perform the BSE calculation. The result is shown in Fig.2. Is it right? )
The attachment is my input files.

Thank you.

Fig.1.JPG

Fig.1 Calculated absorption spectra of MgO http://nano-bio.ehu.es/optical-properti ... el-sup-sup pp.304

Fig.2.JPG

Fig.2 calculated absorption spectra (a) and the oscillator strength (b) of MgO (primitive cell) using Yambo. Red line: G0W0+BSE;Dark dash line: experiment data.

Fig.3.JPG

Fig.3 Real (a) and imaginary (b) parts of the dielectric fucntion of rs-MgO, including excitonic and local-field effects(blue line), the black line is the experiment data.
http://www.ifto.uni-jena.de/~schleife/p ... tation.pdfp.48


Qiaofen Li
qiaofen0630@163.com
School of Electronic Science and Engineering
Southeast University
2# SiPaiLou
Nanjing
Jiangsu, China

[myrta gruning]

Dear Quiaofen Li

In this article,
PHYSICAL REVIEW B 80, 035112
and probably in Schleife dissertation, you can find the answer to both your questions.
They discuss thoroughly both the convergence with the k-point and the "trick" they use to converge the exciton , both the underestimation of the gap in GW calculations
(see references 17 A. Schleife et al., J. Korean Phys. Soc. 53, 2811; 19 A. R. H. Preston, B. J. Ruck, L. F. J. Piper, A. DeMasi, K. E. Smith, A. Schleife, F. Fuchs, F. Bechstedt, J. Chai, and S. M.
Durbin, Phys. Rev. B 78, 155114)

Best,
Myrta