Doubt in Si Spectrum

[muthu]

file1.txt

file3.txt

file2.txt

Dear users
i new to yambo. just i have installed yambo-3.3.0-rev41 and tried to run it for optical spectrum. i did this calculation by typing the following one by one

p2y -N yambo -N yambo -o c yambo -N

i dont know whether this is correct or wrong?
i obtained spectrum by plotting data ( col 1 vs col 2) in o.eps_q1_inv_rpa_dyson file.( i attached below also the output files)
i have one question in addition to above si has band gap 0.7ev but peak appears at above 2 ev and new one above 3ev. why?
this is why i doubt in my calculation
i request all to clarify this problem

step1:
physics@physics-mku:~/tmp/si.save$ /home/physics/yambo/bin/p2y -N
__ __ _______ __ __ _______ _______
| | | || _ || |_| || _ || |
| |_| || |_| || || |_| || _ |
| || || || || | | |
|_ _|| || || _ | | |_| |
| | | _ || ||_|| || |_| || |
|___| |__| |__||_| |_||_______||_______|

<---> P(W) 2 Y(ambo) Ver. 5.0
<---> DBs path set to .
<---> Index file set to data-file.xml
<---> Header/K-points/Energies...done
<---> Cell data...done
<---> Atomic data...done
<---> Symmetries...[SI no]......[-I no]...[TR yes]
<---> XC functional...Slater exchange(X)+Perdew & Zunger(C)
<---> K-points mesh...done
<---> RL vectors...done
<---> IGK arrays...done
<---> Energies...done
<---> :: Electrons : 8.000000
<---> :: Temperature [ev]: 0.000000
<---> :: Lattice factors [a.u.]: 5.100000 5.100000 5.100000
<---> :: K-points : 1
<---> :: Bands : 8
<---> :: Spinor components : 1
<---> :: Spin polarizations : 1
<---> :: Spin orbit coupling : no
<---> :: Symmetries [spatial]: 24
<---> :: [T-rev]: yes
<---> :: Max WF components : 537
<---> :: RL vectors (WF): 537
<---> :: RL vectors (CHARGE): 4477
<---> :: XC potential : Slater exchange(X)+Perdew & Zunger(C)
<---> :: Atomic species : 1
<---> :: Max atoms/species : 2
<---> == Writing DB1 ...done ==
<---> == DB2 (wavefunctions) ...done ==
<---> == P2Y completed ==


Step2:
physics@physics-mku:~/tmp/si.save$ /home/physics/yambo/bin/yambo -N
_| _| _|_| _| _| _|_|_| _|_|
_| _| _| _| _|_| _|_| _| _| _| _|
_| _|_|_|_| _| _| _| _|_|_| _| _|
_| _| _| _| _| _| _| _| _|
_| _| _| _| _| _|_|_| _|_|

<---> [01] Files & I/O Directories
<---> [02] CORE Variables Setup
<---> [02.01] Unit cells
<---> [02.02] Symmetries
<---> [02.03] RL shells
<---> Shells finder |####################| [100%] --(E) --(X)
<---> [02.04] K-grid lattice
<---> [02.05] Energies [ev] & Occupations
<---> [03] Transferred momenta grid
<---> X indexes |####################| [100%] --(E) --(X)
<---> SE indexes |####################| [100%] --(E) --(X)
<---> [04] Game Over & Game summary

step 3:
physics@physics-mku:~/tmp/si.save$ /home/physics/yambo/bin/yambo -o c
#
# ::: ::: ::: :::: :::: ::::::::: ::::::::
# :+: :+: :+: :+: +:+:+: :+:+:+ :+: :+: :+: :+:
# +:+ +:+ +:+ +:+ +:+ +:+:+ +:+ +:+ +:+ +:+ +:+
# +#++: +#++:++#++: +#+ +:+ +#+ +#++:++#+ +#+ +:+
# +#+ +#+ +#+ +#+ +#+ +#+ +#+ +#+ +#+
# #+# #+# #+# #+# #+# #+# #+# #+# #+#
# ### ### ### ### ### ######### ########
#
# GPL Version 3.3.0 Revision 1887
# http://www.yambo-code.org
#
optics # [R OPT] Optics
chi # [R CHI] Dyson equation for Chi.
% QpntsRXd
1 | 1 | # [Xd] Transferred momenta
%
% BndsRnXd
1 | 8 | # [Xd] Polarization function bands
%
NGsBlkXd= 1 RL # [Xd] Response block size
% EnRngeXd
0.00000 | 10.00000 | eV # [Xd] Energy range
%
% DmRngeXd
0.10000 | 0.10000 | eV # [Xd] Damping range
%
ETStpsXd= 100 # [Xd] Total Energy steps
% LongDrXd
1.000000 | 0.000000 | 0.000000 | # [Xd] [cc] Electric Field
%

Step4:
physics@physics-mku:~/tmp/si.save$ /home/physics/yambo/bin/yambo -N

____ ____ ___ .___ ___. .______ ______
\ \ / / / \ | \/ | | _ \ / __ \
\ \/ / / ^ \ | \ / | | |_) | | | | |
\_ _/ / /_\ \ | |\/| | | _ < | | | |
| | / _____ \ | | | | | |_) | | `--" |
|__| /__/ \__\ |__| |__| |______/ \______/

<---> [01] Files & I/O Directories
<---> [02] CORE Variables Setup
<---> [02.01] Unit cells
<---> [02.02] Symmetries
<---> [02.03] RL shells
<---> [02.04] K-grid lattice
<---> [02.05] Energies [ev] & Occupations
<---> [03] Transferred momenta grid
<---> [04] Optics
<---> Dipole (T): |####################| [100%] --(E) --(X)
<---> [WARNING] Missing non-local pseudopotential contribution
<---> [X-CG] R(p) Tot o/o(of R) : 4 16 100
<---> [FFT-X] Mesh size: 12 12 12
<---> Xo@q[1] 1-100 |####################| [100%] --(E) --(X)
<---> X @q[1] 1-100 |####################| [100%] --(E) --(X)
<---> [05] Game Over & Game summary

Here
File1- o.eel_q1_inv_rpa_dyson
file2 - o.eps_q1_inv_rpa_dyson
file3- r_optics_chi

[Daniele Varsano]

Dear Muthu,
as a general comments, electronic gap (measurable by phototemission) and optical gap (absorption) are two different quantities, so they do not have to coincide.
The procedure you used is correct to calculate optical spectrum in linear response (independnent particle approximation or RPA with inclusion of local field effects) but several problems I can see in your calculation. Please note (see the report file 3) your gap is 2.13eV and not 0.7eV. From the report file I can see that you have calculated from the ground state only one Kpoint (gamma), and this is clearly unreliable. I do not know if this come from your quantum-espresso wrong input file, or in the yambo conversion, but from the p2y standard output reported above, mostly your qe input file. Last comment, in your input file I can see "NGsBlkXd= 1 RL", if you want to take into account local field effects, this should be raised, ie taken at convergence. Also the 8 bands you considered probably are not not enough.
Finally RPA it is not a very good approximation for Silicon, in order to reproduce experiments you should rely on the GW/BSE approach. I strongly suggest you to take your time and have a careful look at the tutorial, the GW tutorial it is on Silicon.

Hope it helps,
Daniele

[muthu]

Thank you Daniele for your quick reply
i will go through my qe input file for any error. but i do not know how to increase

NGsBlkXd= 1 RL

i request you to guide me in this issue

thank you

[Daniele Varsano]

Dear Muthu,
NgsBlkXd are the block of the response function to be diagonalized in reciprocal space. This variable, as well as the number of bands etc, have to be increased until convergence. The general procedure is to perform different runs increasing this value (e.g. 50, 100, 200 ....etc) until your final results does not change anymore in the range of the accuracy you want. Regarding the convergence issue I strongly suggest you to follow the tutorials. Anyway, beside to converge this variable, the number of the k-points in your ground state calculation have to be set up to a reasonable value, otherwise you will not get reasonable results.

Best,
Daniele

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