Coulomb Cutoff

[martinspenke]

Dear Daniele,

Two questions concerning Coulomb Cut-off :
1) Should one use Coulomb Cut-off technique both in GW AND BSE calculation
or is it enough having used it once in GW calculation for converging quasi particle energies ?
2) Is it generally better to use a box or sphere (because of its analytical nature) for isolated molecules ?

Regards
Martin

[Daniele Varsano]

Dear Martin,
it is important to cut the interaction in the screening, so it is useful to introduce it also in the BSE, even if the bigger effect are in the GW calculations as you can see in PHYSICAL REVIEW B 73, 205119 2006. Anyway, you need to calculate it once for all at the beginning, next the code will read the database, provided it is indicated in the input with the same geometry.
If your geometry is permits it I suggest you to use the sphere, being analytical as you said, it is more accurate. In the case you need to use the box, please be aware to set the edge of the box in input the double on what you need (this is related to an internal function of the code still needed to be fixed). This is reported in several post in the forum.

Best,
Daniele