About BSENGBlk and NGsBlkXs settings

[hplan]

Dear Developers:

I did several tests on bulk silicon playing with some keywords like BSENGBlk and BSEBands, and have a confusion about BSENGBlk. I found the value of BSENGBlk given in the end of output data was not consistent with my previous setting in yambo.in , though the value of NGsBlkXs was larger than this value.
For instance, i did a emls calculation with NGsBlkXs=89 RL first, and performed BSE calculation with BSENGBlk=89. But after calculation , I found the actual value of calculation was 65 RL. I should misunderstand the relationship between BSENGBlk and NGsBlkXs. Would you please explain some detailed instruction for this ? Is there any empirical rule for these two keywords ?

Cheers,
Hai-Ping

[myrta gruning]

Hello Hai-Ping

regarding the BSENGBlk I refer to this old post:

Re: crash for large values of BSENGBlk
Postby myrta gruning » Mon Mar 30, 2009 7:21 pm

Note that you cannot choose such "large" values for BSENGBlk. If you look at the expression of the coupling part in reciprocal space that is given in the yambo documentation
http://www.yambo-code.org/doc/docs/doc_BSK.php
you see you have sums q+G appearing. Then, the maximum G you can choose is limited by the fact that the vector resulting from the sum with the largest q has to be in the sphere defined by your cutoff.

The code checks whether the chosen value for BSENGBlk is compatible with the other parameters, and in the case is too large will resize it to the maximum possible value and write a warning to the standard output and report file: you should get a message/warning in the l_*/r_* such as ' W size reduced due to symmetry constraints' or '[BSE-W] W size forced by symmetry to be :'.

I hope this answer your question (if not please attach the inputs/outputs of a specific case)
Cheers

m