[Pw_forum] transmission calculation

[Gabriele Sclauzero]

Quoting Manoj Srivastava <manoj at phys.ufl.edu>:

> Dear PWSCF users and developers,
>  I have been trying to do the conductance calculation for the twin
> boundary of Cu. I compared my results with previously done calculations
> and for most K points the transmission coefficients match up very well.
> But there are some k points that I get transmission coefficients more than
> 1! This is not reasonable, as the maximum value of transmission
> coefficient could be 1.I am getting 1.000345, and similar for other k
> points.

Which k-points? How many channels are there? Please send me the output  
file or post the relevant part of it.


> Do you think transmission coefficients being more than 1 is just
> numerical error of the code or there is something wrong with my input
> file? Attached is the input file for lead and scatterign region -

Transmission coefficients should be between 0 and 1. In the code there  
are many levels of approximation. Some of them may affect the results.  
Usually the two relevant parameters one needs to adjust are epsproj  
and ewind. Why are you tweaking the others? Have you tried the default?




>     ecutwfc =150.0,

Why such a high value? You are using US, aren't you?



> ATOMIC_POSITIONS
>   Cu  0.0   0.0                0.0
>   Cu -0.5   0.288675134        0.81649658
>   Cu -1.0   0.577350269        1.632993162
>
> K_POINTS (automatic)
> 6 6 8 1 1 1
> CELL_PARAMETERS {hexagonal}
>  1.0   0.0    0.0
> -0.5   0.8660254037844386 0.0
>  0.0   0.0     2.449489743

This shouldn't be an issue, but you could try to use ibrav=4 instead  
of ibrav=0 and specify atomic positions such that all atoms are inside  
the first primitive cell (i.e. the one with R=0)





>
>  /
>   6
>   0.5000000     -0.5000000               1
>   4.2584095E-17  0.5000000               1

Why don't you specify 0.00000 instead? Should not matter anyway.


Gabriele Sclauzero


SISSA & Democritos


>   0.250000000    0.0000000               1
>   0.1666667      0.1666667               1
>  -1.2775231E-16 -0.2500000               1
>   0.2500000     -0.2500001               1
> 1
> 0.0
>
>
> Regards,
> Manoj Srivastava
> University of Florida,
> Gainesville, FL
>
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