by **brsahu** » Wed Jul 15, 2009 7:13 am

Dear Andrea,

To get the quasiparticle gap in bulk silicon with GW, I did the following,

1) scf and nscf run (with pwscf),both with 8x8x8 k-points with no shifts. There are 29 k-points in the IBZ including number of k points= 29 including the Gamma point:

cart. coord. in units 2pi/a_0

k( 1) = ( 0.0000000 0.0000000 0.0000000), wk = 0.0039062

k( 2) = ( -0.1250000 0.1250000 -0.1250000), wk = 0.0312500

k( 3) = ( -0.2500000 0.2500000 -0.2500000), wk = 0.0312500

k( 4) = ( -0.3750000 0.3750000 -0.3750000), wk = 0.0312500

k( 5) = ( 0.5000000 -0.5000000 0.5000000), wk = 0.0156250

k( 6) = ( 0.0000000 0.2500000 0.0000000), wk = 0.0234375

k( 7) = ( -0.1250000 0.3750000 -0.1250000), wk = 0.0937500

k( 8) = ( -0.2500000 0.5000000 -0.2500000), wk = 0.0937500

k( 9) = ( 0.6250000 -0.3750000 0.6250000), wk = 0.0937500

k( 10) = ( 0.5000000 -0.2500000 0.5000000), wk = 0.0937500

k( 11) = ( 0.3750000 -0.1250000 0.3750000), wk = 0.0937500

k( 12) = ( 0.2500000 0.0000000 0.2500000), wk = 0.0468750

k( 13) = ( 0.0000000 0.5000000 0.0000000), wk = 0.0234375

k( 14) = ( -0.1250000 0.6250000 -0.1250000), wk = 0.0937500

k( 15) = ( 0.7500000 -0.2500000 0.7500000), wk = 0.0937500

k( 16) = ( 0.6250000 -0.1250000 0.6250000), wk = 0.0937500

k( 17) = ( 0.5000000 0.0000000 0.5000000), wk = 0.0468750

k( 18) = ( 0.0000000 0.7500000 0.0000000), wk = 0.0234375

k( 19) = ( 0.8750000 -0.1250000 0.8750000), wk = 0.0937500

k( 20) = ( 0.7500000 0.0000000 0.7500000), wk = 0.0468750

k( 21) = ( 0.0000000 -1.0000000 0.0000000), wk = 0.0117188

k( 22) = ( -0.2500000 0.5000000 0.0000000), wk = 0.0937500

k( 23) = ( 0.6250000 -0.3750000 0.8750000), wk = 0.1875000

k( 24) = ( 0.5000000 -0.2500000 0.7500000), wk = 0.0937500

k( 25) = ( 0.7500000 -0.2500000 1.0000000), wk = 0.0937500

k( 26) = ( 0.6250000 -0.1250000 0.8750000), wk = 0.1875000

k( 27) = ( 0.5000000 0.0000000 0.7500000), wk = 0.0937500

k( 28) = ( -0.2500000 -1.0000000 0.0000000), wk = 0.0468750

k( 29) = ( -0.5000000 -1.0000000 0.0000000), wk = 0.0234375

----------------------------------------------

You can see there is no X-point with coordinate (1,0,0) in the chosen set of k-points. Need a X-point to calculate the QP correction and the indirect gap.

2) then invoked 'p2y -N' to generate the core database files file.db1 and flle.wf in the SAVE directory.

3) invoked yambo -i and then yambo -g n -p p to generate the the starting input.

4) Changed the paramters % BndsRnXp, NGsBlkXp, %QPkrange in the default ' yambo.in' :

--------------------------------------

gw0 # [R GW] GoWo Quasiparticle energy levels

ppa # [R Xp] Plasmon Pole Approximation

xxvxc # [R XX] Hartree-Fock Self-energy and Vxc

em1d # [R Xd] Dynamical Inverse Dielectric Matrix

EXXRLvcs= 7391 RL # [XX] Exchange RL components

% QpntsRXp

1 | 29 | # [Xp] Transferred momenta

%

% BndsRnXp

1 | 60 | # [Xp] Polarization function bands

%

NGsBlkXp= 169 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 | 200 | # [GW] G[W] bands range

%

GDamping= 0.10000 eV # [GW] G[W] damping

QPreport= "kpbne0ees0" # [GW] QP info. Keys: kp/bn/xx/xc/s0/sq/e0/eq/ee/zf/ds/lm/lf

%QPkrange # [GW] QP generalized Kpoint/Band indices

1| 1| 1| 10|

21| 21| 1| 10|

%

%QPerange # [GW] QP generalized Kpoint/Energy indices

% 1| 21| 6.2302|6.8605|

------------------------------

There is point (0,-1,0) i.e. k(21) which is the vector in y direction. I assumed that since the system is cubic, X, Y, Z are equivalent directions and therefore chose point 21 and point 1 from the above set, each with 10 bands to be between Gamma

In the entry %QPerange, the last two numbers are energy of the highest occupied band at first k-point ie Gamma and the lowest unoccupied band at 'Y' point ie 21st k-point from the above k-point set.

is the format of this entry correct: first k-point/second k-point/energy for highest occupied band at first k-point/energy for lowest unoccupied band at the second kpoint ?

Then invoked 'yambo' in parallel:

got the file o.qp, which has the entries

----------------------------------------------------------------

Kpt Band Eo E-Eo Sc(Eo)

#

1.00000 1.00000 -12.05084 -0.08216 6.73922

1.000000 2.000000 0.000000 -0.556002 0.504326

1.000000 3.000000 0.000000 -0.556009 0.504327

1.000000 4.000000 0.000000 -0.556012 0.504327

1.000000 5.000000 2.570040 0.123556 -4.044952

1.000000 6.000000 2.570040 0.123564 -4.044961

1.000000 7.000000 2.570040 0.123577 -4.044949

1.00000 8.00000 3.47699 0.07209 -4.73022

1.000000 9.000000 7.768295 0.307703 -5.378475

1.00000 10.00000 7.76830 0.30768 -5.37848

21.00000 1.00000 -7.83877 -0.43612 4.39779

21.00000 2.00000 -7.83877 -0.43615 4.39779

21.00000 3.00000 -2.90341 -0.57803 1.72195

21.00000 4.00000 -2.90341 -0.57805 1.72195

21.00000 5.00000 0.63032 0.13899 -3.61636

21.00000 6.00000 0.63032 0.13898 -3.61636

21.00000 7.00000 10.15438 -0.10730 -6.95247

21.00000 8.00000 10.15438 -0.10729 -6.95249

21.00000 9.00000 10.95771 0.08799 -6.41683

21.00000 10.00000 10.95771 0.08798 -6.41683

----------------------------

What is the meaning of E_0, E-E_0 and sc(E_0) above?

It is the 4th band at Gamma (first k-point) which is highest occupied state and 5th band at k-point 21 which is lowest occupied. Based on the definitions of the parameters

E_0, E-E_0 etc, the difference of 4th and 5th band. at these two k-points 1 and 21, will give the indirect gap between X (or Y) and Gamma.

Is the analysis correct:

5) Your Yambo paper says the indirect gap of 1.20 eV was obtained close to expt value of 1.17 eV. I do not know whether I am getting it or not. Only after I know the meanings of E_0, E-E_0 etc, then the indirect gap can be known for the above result.

Sahu

2) r_setup is not written in the parallel run.