Dear PWSCF users,
I have a question regarding real band structure calculated from
PWCOND. Complex band code requires kx,ky and E as input and gives kz
as output. I have noticed that the answer for kz depends whether you have
unit cell vectors as (a1,a2,a3) or (a1,a2,-a3). I did a calculation for
Cu(001) with 2 atoms tetragonal unit cell, with the following input file -
& control
calculation='scf'
pseudo_dir = '/home/manoj/espresso-4.0.1/pseudo',
outdir='./',
prefix='cu',
/
&system
ibrav = 0,
celldm(1)=4.7588286373854648
nat= 2,
ntyp= 1,
ecutwfc =150.0,
occupations='smearing',
smearing='gaussian',
degauss=0.02,
ecutrho=400
/
&electrons
conv_thr = 1.0e-8
mixing_beta=0.7
/
ATOMIC_SPECIES
Cu 63.55 Cu.pz-d-rrkjus.UPF
ATOMIC_POSITIONS
Cu 0.0 0.0 0.0
Cu 0.5 0.5 0.707106781
K_POINTS (automatic)
8 8 8 1 1 1
CELL_PARAMETERS
1.0 0.0 0.0
0.0 1.0 0.0
0.0 0.0 1.414213562
&inputcond
outdir='./'
prefixl='cu'
band_file ='bands.cu'
ikind=0
energy0=2.d0
denergy=-0.5
ewind=104.d0
epsproj=1.d-6
/
1
0.0 0.0 1.0
24
This gives me reasonable answer and it matches up with existing results.
Now when I changed a3 to -a3, so that the unit cell now has become
(a1,a2,-a3), the answer does not match up with the previous one.
Just to give you one concrete example-
at Fermi energy for kx,ky (0,0) for unit cell (a1,a2,a3) we get kz=-0.1571
while for (a1,a2,-a3) we get kz=0.07323.
I understand that for two different set of unit cell vectors we should not
in general expect k_z to match, but this is a very special example, as it
is just mirror symmetry about xy plane. so shouldn't kz in one set have
value -kz in other?
Thanks for your attention.
Regards,
Manoj Srivastava
Department of Physics
University of Florida
Gainesville, FL