Yambo Community Forum

Dear all,
When calculating the K-points convergence in the section "COHSEX without empty bands" on the Yambo homepage (https://wiki.yambo-code.eu/wiki/index.php?title=Silicon), I am unable to obtain the same bandgap as shown in the image on the homepage. I am puzzled by the data extraction script file provided below, named parse_gap.sh( which was obtained from the folder \Silicon\YAMBO\.References ). For the *-Cohsex* calculations, why does it output $4+$5, which seems to imply that the bandgap is calculated as CBMo + CBM? Shouldn't it be necessary to subtract (VBMo+VBM) as well?
#!/bin/bash
if [ ! -f GAMMA/References/$1 ]
then
echo "File not found"
exit
fi
rm -f $2
kpts='GAMMA 2x2x2 4x4x4 6x6x6 8x8x8'
NK=(1 8 64 216 512)
j=0
for i in ${kpts}
do
VBMo=`grep " 1.000" $i/References/$1 | grep " 4.0000" | grep " 0.000" | awk '{print $3}'`
VBM=`grep " 1.000" $i/References/$1 | grep " 4.0000" | grep " 0.000" | awk '{print $4}'`
CBMo=`grep " 2.576" $i/References/$1 | grep " 5.000" | awk '{print $3}'`
CBM=`grep " 2.576" $i/References/$1 | grep " 5.000" | awk '{print $4}'`
case "$1" in
*-01HF*)
echo ${NK[$j]} $VBMo $VBM $CBMo $CBM | awk '{print $1 " " $5-$3 }' >> "$2"
;;
*)
echo ${NK[$j]} $VBMo $VBM $CBMo $CBM | awk '{print $1 " " $4+$5 }' >> "$2"
;;
esac
j=`expr $j + 1`
done


To further illustrate my issue, I have found a specific example case:
The calculation results in the file o-Cohsex_HF7Ry_X0Ry-nb10.qp, which was obtained from the folder \Silicon\YAMBO\4x4x4\.References provided by Yambo, are as follows:
# K-point Band Eo E-Eo Sc|Eo
#
...
1.000000 4.000000 0.000000 0.411350 1.732646
1.000000 5.000000 2.576077 1.659489 -2.763862
...
I believe the formula to calculate the bandgap should be:
2.576077+1.659489-(0.000000+0.411350) = 3.824216
However, the result in the file Cohsex_HF7Ry_X0Ry-nb10_gap_vs_kpoints, which was obtained from the folder \Silicon\YAMBO\.References provided by Yambo, is:
64 4.23557
It indicates that the formula for calculating the bandgap is:
2.576077+1.659489 = 4.23557
Why is there such a discrepancy? Could you please clarify the correct formula for calculating the bandgap in COHSEX and PPA?

Looking forward to your response.
Best wishes,
Xiao

Dear Xiao,

these are old tutorials, the scripts to extract quantities were done according to old yambo output formats. Do not stick on that.
Anyway, what you are obtaining is correct.

Consider also to have a look at tutorials of recent schools.

Best,
Daniele