[Pw_forum] transmission calculation

[Gabriele Sclauzero]

Manoj Srivastava wrote:
> Dear PWSCF users and developers,
>  I have tried to do a transmission calcuation and not getting right
> results. I have tried to figure out the reason behind this and realized
> that in my set up for some reason the Bloch waves in left lead get changed
> resulting wrong transmission. By this I meant that, if I just try to
> calculate complex band of the left lead, I have a kz for each kx,ky and E
> but when I am doing transmission calculation, the Bloch's wave in the same
> lead has different kz for the same kx,ky and E, which does not make sense
> as why should the Bloch's wave in lead get affected by the presence of
> scattering region? For the right lead kz remains the same in both cases
> though, which I believe how it should be. 

Does it happen also when you do not use G_perp basis reduction? Can you try again the CBS 
and the transmission calculation without specifying ecut2d, nz1 and putting ewind=1.d3?

Better, first check the size of the reduced basis using

grep n2d <output file from transmission> <output file from CBS>

and see if they are very different (or if the second is too low with respect to the size 
of the whole basis set).
Also try to understand which of the two results (kz vectors) is correct, by comparing the 
real part of kz with the band structure from pw.x


GS


>  I did this for several cases, I interchanged right and left leads,
> increased number of atoms in the scattering region, chose scattering
> region in different way, and everytime kz of left lead changes. Following
> is my input file for the scattering region - 
> 
> scf part -
> 
> &control
>     calculation='scf'
>     pseudo_dir = '/home/manoj/espresso-4.0.1/pseudo',
>     outdir='./',
>     prefix='cus',
>  /
>  &system
>     ibrav =0,
>     celldm(1)=4.82,
>     nat= 10,
>     ntyp= 1,
>     ecutwfc =50.0,
>     occupations='smearing',
>     smearing='gaussian',
>     degauss=0.02,
>     ecutrho=500
>  /
>  &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   0.288675134 0.816496581
>   Cu -1.0   0.577350269 1.632993162
>   Cu -1.5   0.866025404 2.449489743
>   Cu  0.0   0.0         3.265986324
>   Cu  0.5  -0.288675134 4.082482905
>   Cu  1.0  -0.577350269 4.898979486
>   Cu  1.5  -0.866025404 5.715476066
>   Cu  1.0  -0.577350269 6.531972647
>   Cu  0.5  -0.288675134 7.348469228
>  K_POINTS (automatic)
> 6 6 4 1 1 1
> CELL_PARAMETERS {hexagonal}
>  1.0   0.0         0.0
> -0.5   0.866025403 0.0
>  0.0   0.0         8.16496581
> 
> 
> 
> conductance part -
> 
> &inputcond
>     outdir='./'
>     prefixl='cul'
>     prefixr='cur'
>     prefixs='cus'
>     tran_file ='trans.twin'
>     ikind=2
>     ecut2d=50
>     energy0=0.0
>     denergy=0.0
>     ewind=5.d0
>     epsproj=1.d-6
>     nz1=25
>  /
>   2
>   0.000000       0.000000               1
>   0.5000000     -0.5000000               1
> 
> 1
> 0.0
> 
> Thank you for your attention. 
> 
> Regards, 
> Manoj Srivastava
> Graduate Student
> Department of Physics
> University of Florida, Gainesville, FL
> 
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> 

-- 


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| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
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| email: sclauzer at sissa.it                         |
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