# [Pw_forum] PWCOND

Alexander Smogunov smogunov at sissa.it
Wed Apr 22 13:00:01 CEST 2009

```The leads are semi-infinite in the scattering problem set-up
when they are connected by a scattering region.
To find the scattering states you need the generalised Bloch
states in the parts of leads (their unit cells) adjacent to the
scattering region. These you calculate from INFINITE leads taking the
unit cell ...
You can have a look at my home page (still very draft), where there are
some notes and examples in pwcond section.
Alexander.

В Срд, 22/04/2009 в 06:31 -0400, Manoj Srivastava пишет:
> 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
>
>
> В Втр, 21/04/2009 в 23:44 -0400, Manoj Srivastava пишет:
> > 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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> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
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--
Alexander Smogunov
Email:     smogunov at sissa.it