with&without truncation

[WEI Wei]

Dear All,

I have done a QP calculation with box-shaped Coulomb interaction (yambo -c -g n -p p), it gave the first valence band and the first conduction band at one k point as:
----------------------------------------------------------------

K-point Band Eo E-Eo Sc(Eo)
... ...
1.00000 17.00000 -0.66979 -0.79705 1.23180
1.00000 18.00000 3.38593 1.79275 -2.39824
... ...
----------------------------------------------------------------
However, without the box-shaped Coulomb interaction (yambo -g n -p p), it gave:
----------------------------------------------------------------
K-point Band Eo E-Eo Sc(Eo)
... ...
1.00000 17.00000 -0.66979 -1.54338 2.06721
1.00000 18.00000 3.38593 1.01423 -3.22978
... ...
----------------------------------------------------------------

The result seems strange a little bit, i.e., truncated Conlomb interaction just shift the conduction and valence bands simultaneously and thus does not improve the band gap. So can you please tell me what was wrong with my calculation?
Thank you very much!

[claudio]

Dear WEI Wei

may you put in the forum the two inputs you used for the calculations,

claudio

[WEI Wei]

Dear Claudio,

Thank you for you reply!

yambo -c -g n -p p
------------------------------------------------------------------------------------------------
rim_cut # [R RIM CUT] Coulomb interaction
gw0 # [R GW] GoWo Quasiparticle energy levels
ppa # [R Xp] Plasmon Pole Approximation
HF_and_locXC # [R XX] Hartree-Fock Self-energy and Vxc
em1d # [R Xd] Dynamical Inverse Dielectric Matrix
RandQpts=1000000 # [RIM] Number of random q-points in the BZ
RandGvec=1 RL # [RIM] Coulomb interaction RS components
CUTGeo= "box z" # [CUT] Coulomb Cutoff geometry: box/cylinder/sphere
% CUTBox
0.000 | 0.000 | 25.056 | # [CUT] [au] Box sides
%
CUTRadius= 0.000000 # [CUT] [au] Sphere/Cylinder radius
CUTCylLen= 0.000000 # [CUT] [au] Cylinder length
EXXRLvcs= 13787 RL # [XX] Exchange RL components
% QpntsRXp
1 | 91 | # [Xp] Transferred momenta
%
% BndsRnXp
1 | 300 | # [Xp] Polarization function bands
%
NGsBlkXp= 400 RL # [Xp] Response block size
% LongDrXp
1.000000 | 0.000000 | 0.000000 | # [Xp] [cc] Electric Field
%
PPAPntXp= 27.21138 eV # [Xp] PPA imaginary energy
% GbndRnge
1 | 300 | # [GW] G[W] bands range
%
GDamping= 0.100000 eV # [GW] G[W] damping
dScStep= 0.100000 eV # [GW] Energy step to evalute Z factors
DysSolver= "n" # [GW] Dyson Equation solver (`n`,`s`,`g`)
%QPkrange # [GW] QP generalized Kpoint/Band indices
1| 91| 13|27|
%
%QPerange # [GW] QP generalized Kpoint/Energy indices
1| 91| 0.0|-1.0|
%
------------------------------------------------------------------------------------------------

yambo -g n -p p
------------------------------------------------------------------------------------------------
gw0 # [R GW] GoWo Quasiparticle energy levels
ppa # [R Xp] Plasmon Pole Approximation
HF_and_locXC # [R XX] Hartree-Fock Self-energy and Vxc
em1d # [R Xd] Dynamical Inverse Dielectric Matrix
EXXRLvcs= 13787 RL # [XX] Exchange RL components
% QpntsRXp
1 | 91 | # [Xp] Transferred momenta
%
% BndsRnXp
1 | 300 | # [Xp] Polarization function bands
%
NGsBlkXp= 400 RL # [Xp] Response block size
% LongDrXp
1.000000 | 0.000000 | 0.000000 | # [Xp] [cc] Electric Field
%
PPAPntXp= 27.21138 eV # [Xp] PPA imaginary energy
% GbndRnge
1 | 300 | # [GW] G[W] bands range
%
GDamping= 0.100000 eV # [GW] G[W] damping
dScStep= 0.100000 eV # [GW] Energy step to evalute Z factors
DysSolver= "n" # [GW] Dyson Equation solver (`n`,`s`,`g`)
%QPkrange # [GW] QP generalized Kpoint/Band indices
1| 91| 13|27|
%
%QPerange # [GW] QP generalized Kpoint/Energy indices
1| 91| 0.0|-1.0|
%
------------------------------------------------------------------------------------------------

Thanks.

[Daniele Varsano]

Dear Wei Wei,
the use of the coulomb cutoff, by its nature, needs systematic tests.
The size of the cut radius/side depends on both the size of the system
and the supercell (i.e. the vacuum region).
Even if not well documented , it is extensively discussed in the forum.
If I'm not wrong in the case of the box, the zcut values have to be put,
around twice the size of your system (I have to check, and eventually correct it
as it is controintuitive), and next the vacuum have to be set accordingly.
I do not know the size of your system so I cannot say nothing about your inputs,
anyway be sure from the report, that the screening and HF are recalculated
and not just read when changing input.
moreover it works only on simple orthorhombic unit cells.

Cheers,
Daniele

[WEI Wei]

Dear Daniele,

Thank you very much for your comments!
I will test it in next days.

Thanks.