Dear Wachr,
By default, this is not printed out in the output files. Can one access the dielectric function, which enters into GW, by reading the em1d-file* written out by yambo? Or does one have to perform an extra RPA-calculation?
The dielectric screening is a matrix, \epsm1(G,G1)_q, according to your input parameters it is a 600x660 matrix for each q point (41 points), so in my opinion an output for that will be useless.
How does the cylindrical cutoff of my system affect the dielectric function?
Which components of the matrix you want to look at? In some publications, including our paper on the cutoff it is plotted just the head \epsm1_00(q), this can be done
either looking at the epsm1 database unsing ncdump if you are using the netcdf library, but the it can be not trivial to extract the right component, or as you say doing extra RPA calculations (yambo -o g).
(You may find a warning about 'metallic system' in the output - due to smearing. I could circumvent this for later calculations.)
The warning means that if a metallic system is found, interband contribution to the polarization can be added using Drude model, anway in your case, you should have a semi-metal and I do not think that these will be relevant.
Finally, I want to perform a BSE-calculation. As I see, only static screening enters the BSE. Thus, I will have to choose the static screening based on the RPA-screening, including the effect of the cylindrical cufoff.
Yes only static screening, this is the state of the art for BSE calculation, there is the possibility to consider dynamic screening but this part of the code it is not yet included in the GPL release
By the way, I have two technical questions:
As noted in a long post about the Coulomb cutoff, the cutoff-technique may fail for the G-space approach for the the dielectric function using the Dyson-equation. Does this problem also affect the GW calculation itself? (see last page of the cited post)
No, it does not, it is about the macroscopic dilectric functions.
Do I need to specify NonPDirs="XY"? (The tube lies along the z-axis.). Does this option also affect my GW-calculations?
No it is not needed, it just add the dynamic polarizability when doing linear response optics.
A remark from the users perspective: It would be extremely helpful to find information about the output files that yambo will generate on a certain runlevel. It takes a lot of time to find this out - also the exact informations that I find therein [the columns in the output are sparsely documented...]. I know, that nobody likes to write documentation
. It's a lot of work - but I think, many users like me would appreciate this. And it could save your time answering questions in the Forum - on a long-term
.
This is a common remark and as you know it requires a lot of time, and nobody of us is paid for that. We are trying to do our best: about the output there are the tutorials which are fundamental part of the documentations. We have in mind to do a huge improvements in the documentations with the new release but this is a long term task.
Finally two notes about the input you posted:
1) Please note that your input perform HF calculation only, you need to specify when building the input how you want to calculate the screening: Plasmon-pole (add -p p) or a full integration, add (-d)
2) Cutoff, it is better also to specify the variable CUTCylLen, and set it to zero (which means infinite cylinder). Most probably it is set at zero by default, I need to check, anyway if you put it it is safer.
3) %QPkrange , you are calculating corrections for 256 bands 21 kpoints. This is a huge number, and the GW calculations will be very time and memory consuming. Are you sure you need 256 bands corrections. Unless you really need them, you can reduce it to calculate only the bands you are interested in.
Best,
Daniele
