BSE-PPA

[sunxl]

Dear all,

1、yambo -o b -k sex -r -X p -V qp -y d -F bse-1.in and yambo -X s -o b -k sex -y d -V qp -r -F bse-2.in

When I used the above two instructions to generate the BSE input file, I found that one had PPA and the other didn't. Could you please explain what the difference is between the two? The command I used in the gw calculation was "yambo -gw0 p -g n -r -V par -F gw.in", and there was also ppa in it. Does this mean that I should also include ppa in the subsequent gw-bse calculation?

2、When I was calculating BSE, two output files, o-2D_BSE.QP.data and o-2D_BSE.QP.fit, were generated before the calculation was completed. This was an unexpected situation that did not occur in my previous calculations. Could you please explain what these two files represent?


Best,
sunxl

[Daniele Varsano]

Dear sunxl,

1. PPA is needed for GW calculation (dynamical screening), while BSE adopt a static screening.
When doing BSE calculation, you can calculate static screening only (-X s) or use a previous calculated screening (-X p). Database containing dynamical screening also include the static components, and this is the one read by Yambo to build the BSE kernel.
In brief, if you have already done a GW calculation and you have the ndb.pp* databases you can read the static components from there and avoid recalculating.

2. When you correct your KS band with the GW correction for a BSE calculation, Yambo uses the QP previously calculated and perform and interpolation (fit) for the energies that are not present in the database. The two output file contains the GW data you calculated and the fitted data for the rest of the energies.

Best,

Daniele