# [Pw_forum] PWCOND

Manoj Srivastava manoj at phys.ufl.edu
Wed Apr 22 12:31:28 CEST 2009

```Dear Alexander,
Thank you for your quick response. One follow up question on this. So,
how do you describe your left and right leads, if they are different? If
the leads are different then I need to do two calculations for the lead,
one for each leads. They are semi-infinite, so periodicity in one is in +z
direction and while in the other it is in -z direction.

Regards,
Manoj

On
Wed, 22 Apr 2009, Alexander Smogunov wrote:

> Dear Manoj.
The pwcond code was written assuming that the unit cell
starts at z=0 and goes in positive z direction, the direction
of transport. Quite probable that when you invert the
cell it does not work properly...
Alexander

Ð’ Ð’Ñ‚Ñ€, 21/04/2009 Ð² 23:44 -0400, Manoj Srivastava Ð¿Ð¸ÑˆÐµÑ‚:
> 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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--
Alexander Smogunov
Email:     smogunov at sissa.it