How to Accelerate BSE Calculations When Only the Scissor Value Changes

[johannaguzman]

Dear all,

I calculated the linear optical absortion based on the scissor correction.
Can I adjust the scissor value ONLY for the calculation of optical spectrum
and NOT for static dielectric response matrix (X) to avoid recalculating the X?

Best regards.

[Daniele Varsano]

Dear johannaguzman,

please sign your post with your name and affiliation: this is a rule of the forum. You can do once for all by filling your signature in the user profile.

If you apply the scissor operator in the BSE (standard procedure) you do not need to recalculate the screening neither the BSE kernel.
Applying a scissor operator in the screening it is not standard, you can do that and this is used in self consistent GW, but it is quite unusual in BSE as usually provide less accurate results.

In order to change the scissor BSE what you need to do is just to rerun yambo with the new scissor in input pointing to the same directory you calculated previously the BSE kernel databases after having removed (or renamed) the diago database. More explicitly:

1. Input with scissor 1 (input1)
yambo -J bse # BSE kernel databases (ndb.BS_*) will be generated in the bse directory as well as the results of the diagonalization (ndb.BS_diago_*)
2. Change your input with scissor 2 and remove or rename the diago database e.g. mv ./bse/ndb.BS_diago_Q1 ./bse/ndb.BS_diago_Q1_1
run
yambo -J bse

Yambo will read previously generated kernel databases and perform a new diagonalization accounting for the new scissor.

Best,

Daniele