Yambo Community Forum

Dear developers,
I have calculated the band gap of TiO2 within PPA (yambo -g n -p p)
which is 3.6 eV (the experimental value is 3.2 eV)
but the one calculated with full frequency calculations is around 3.8 eV
(with the same parameter used for PPA (k-points, nbndrnge, EXX) but the ETStpsXd is different)
I run these calculations with 3 different ETStpsXd
1-ETStpsXd=100(default one as in the PPA calculations) bandgap=3.84 eV
2-ETStpsXd=200 bandgap=3.80 eV
3-ETStpsXd=600 bandgap=3.82 eV

As you see although I increased the value of ETStpsXd parameter
but the band gap does not decreased !!!
would you please explain me about this problem.
Thanks
S. Ataei, University of Tehran, Iran

Dear S. Atei,
why the PPa approximation and the real axis integration should give exactly the same results? I cant' see the problem.
They are two different implementation, the PPa is an approximation. Next note that in PPA approximation ETStpsXd does not have any sense, it is a single pole approximation, and the model needs only 2 frequencies to fit the dielectric matrix, please have a look to the documentation, so that variable it is not read by the code when calculating the screening in PPA.
Finally note that also the Blocks in G-space (NGsBlkXp) and the bands for the screening (BndsRnXp) need to be converged.
Best,
Daniele