[Pw_forum] PWCOND

Manoj Srivastava manoj at phys.ufl.edu
Wed Apr 22 05:44:30 CEST 2009


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  





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