About the unit in Exxrlvcs

[lesheng]

Hi all,

I am wondering which unit should I use during the calculation. Since in the input file I generated, it uses RL as the unit for EXXRLvcs and NGsBlkXp, but in the first tutorial (Basic concepts of the GW approximation) in Yambo website, it says use Ry instead. So what is the difference?

Thanks for all your attention.

Best,
lesheng

[Daniele Varsano]

Dear Lesheng,
The G vectors can be set in both ways. In RL unit (Reciprocal Lattice unit) you put in your input the numbers of Gvectors you want to use in your calculation. In this way have a control on the "size" of our calculation, while using energy units Ry, all the Gvectors sucht that G^2/2 < E(Ry) are included. In this way the number will depend on the cell size (for instances on the vacuum included in a non 3d periodic calculations), so it is useful when looking at volume effects convergences. You can use both ways, as you feel more confortable. Please note that in the report file you have the correspondence of the shell included for the first and last G-vectors:

Code: Select all

 [02.03] RL shells
  =================

  Shells, format: [S#] G_RL(mHa)

Moreover when using energy units, you will also have the corresponding number of Gvectors in the generated databases showed in the report files.
Hope it helps,

Daniele