LongDrXs & BLongDir CUTBox

[xjxiao]

Dear all，
What is the difference between the parameters LongDrXs (for calculating static screening in Yambo) and BLongDir (for BSE calculations)? How should they be set respectively? Do they need to be set the same?

For 2D materials, when using rim_cut in BSE calculations, what should the third component of CUTBox be set to?

CUTGeo= "box z" # [CUT] Coulomb Cutoff geometry: box/cylinder/sphere X/Y/Z/XY..
% CUTBox
0.00 | 0.00 | 32.0 | # [CUT] [au] Box sides

Thanks！
Xiao

[Daniele Varsano]

Dear Xiao,

LongDrXs: is the long wavelength limit direction for the static screening. A good choice is to average over the meaningful direction (1,1,1) for a bulk (1,1,0) for a 2D material.

BLongDrXs: it depends on which polarization you are interested in. If the system is not homogeneous you can be interested e.g. in 2D in the (100) and (010) separately.

For a 2D material it is recommended to use the shape "slab z" instead of the box which is somehow deprecated. Anyway, if you want to use it this is reported in the
FAQ: https://www.yambo-code.eu/learn/#FAQs

Best,

Daniele