output files analysis

[flybird0303]

Dear all:
I am trying to do the BSE calculation(I performed a runlevel of "yambo -o b -k sex -b -y h"). The folllowing is the input file(yambo.in):

Code: Select all

optics                       # [R OPT] Optics
bse                          # [R BSE] Bethe Salpeter Equation.
bsk                          # [R BSK] Bethe Salpeter Equation kernel
em1s                         # [R Xs] Static Inverse Dielectric Matrix
bss                          # [R BSS] Bethe Salpeter Equation solver
Chimod= "hartree"            # [X] IP/Hartree/ALDA/LRC/BSfxc
BSEmod= "causal"             # [BSE] resonant/causal/coupling
BSKmod= "SEX"                # [BSE] IP/Hartree/HF/ALDA/SEX
BSSmod= "h"                  # [BSS] (h)aydock/(d)iagonalization/(i)nversion/(t)ddft`
BSENGexx=  36729       RL    # [BSK] Exchange components
BSENGBlk= 200            RL    # [BSK] Screened interaction block size
#WehCpl                      # [BSK] eh interaction included also in coupling
% BEnRange
  0.00000 | 6.00000 | eV    # [BSS] Energy range
%
% BDmRange
  0.10000 |  0.10000 | eV    # [BSS] Damping range
%
BEnSteps= 1000                # [BSS] Energy steps
% BLongDir
 1.000000 | 0.000000 | 0.000000 |        # [BSS] [cc] Electric Field
%
% BSEBands
   10 |  15 |                 # [BSK] Bands range
%
% QpntsRXs
  1 | 27 |                   # [Xs] Transferred momenta
%
% BndsRnXs
   1 |  48 |                 # [Xs] Polarization function bands
%
NGsBlkXs= 200            RL    # [Xs] Response block size
% LongDrXs
 1.000000 | 0.000000 | 0.000000 |        # [Xs] [cc] Electric Field
%

In o.eps_q1_haydock_bse, there are 7 columns:

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 E/ev[1]    eps /Im[2] eps /Re[3] eps0/Im[4] eps0/Re[5] eps`/Im[6] eps`/Re[7]

  0.000000   1.143318   7.209290   0.329775   4.457116   1.143318   7.209290
 0.6006E-2   1.174      7.271     0.3348      4.476      1.174      7.271   
   0.01201    1.20510    7.33489    0.34002    4.49580    1.20510    7.33489
   0.01802    1.23797    7.39986    0.34535    4.51556    1.23797    7.39986

My questions:
1. what is the meanings of them? (I know that column(1) corresponds to energy,"eps/Im" corresponds to imaginary part of the dielectric function and "eps/Re" corresponds to real part of the dielectric function. But what is different ?)
2. Are some parameters that I set wrong? (Because what I get are different from the article: http://pubs.acs.org/doi/abs/10.1021/nl403010s ).

The version of Yambo is yambo-3.4.0
Can anyone help me to solve this problem?
Any suggestion is appreicated !
thank you very much!

----------------
Liu Pengfei
PhD student
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences

[Daniele Varsano]

Dear Liu,
1) This is the menaning of the output file:
E/ev[1] eps /Im[2] eps /Re[3] eps0/Im[4] eps0/Re[5] eps`/Im[6] eps`/Re[7]

Imaginary and real part of dilelectric function (column 2 and 3)
Imaginary and real part of the Non-interacting dielectric matrix (useful to look at binding energies when compared with the interacting dielectric function) (comlumn 4 and 5)
Imaginary and real part of dilelectric function for the n-1 Hayfock iteration, they have to be equal/similar to the column 2 and 3 for a converged calculation.



2) Liu, please note that a BSE calculation without taking into account QP energies is meaningless (I suggest you to have a look to some review, there are lectures notes and slides also in the yambo website). And look also at the tutorials.
In order to include them you have to calculate QP energies first, e.g. a GW calculations and input them in the BSE calculation:

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 KfnQPdb= "E < ./SAVE/db.QP"              # [EXTQP BSK BSS] Database 

or ndb.QP if you are linking with netcdf.
If the scissor approximation is valid for your system(something to check) you do not need to calculate the QP correction for all your band/kpoint included in the BSE, but just calculate the correction for the gap and input it in the BSE as:

%KfnQP_E
Delta|1.000000|1.000000| # (EXTQP)(BSK)(BSS) E parameters (c/v) eV|adim|adim
%

Where Delta is the GW correction with respect the KS gap, the other two parameter are the slope for a linear correction of the other k-point/bands if any.
In this way you will shift all the conduction band upward in energy in order to have the right QP gap.

Best,

Daniele