[QE-users] Si band structure using 8 atoms and SC lattice

[Mohamed Saleh]

Dear all,

I have successfully produced the band structure of bulk Si using FCC lattice with 2 atoms per basis. The relevant input sections are as follows:

&system
ibrav=2,
celldm(1)=10.410909236,
nat=2,
ntyp=1,
nbnd=8
/

ATOMIC_POSITIONS (alat)
Si 0.00 0.00 0.00
Si 0.25 0.25 0.25

However, when I try to get the same band structure using a SC unit cell that contain 8 Si atoms, I get completely wrong results. The relevant input sections are as follows:

&system
ibrav=1,
celldm(1)=10.3557,
nat=8,
ntyp=1,
nbnd=32
/

ATOMIC_POSITIONS (alat)
Si 0 0 0
Si 0 0.5 0.5
Si 0.5 0.5 0
Si 0.5 0 0.5
Si 0.75 0.25 0.75
Si 0.25 0.25 0.25
Si 0.25 0.75 0.75
Si 0.75 0.75 0.25

Both calculations use the same special k-points. The resulting band structures (the correct one and the wrong one) are attached. So what am I doing wrong?

Thanks in advance


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