Reproducing NEGF results

[Michael LaCount]

I am trying to reproduce the transmission coefficient plot found in Figure 4 of the CP2K Electron Transport based on Non-Equilibrium-Greens-Functions Method: eCSE 08-09 Technical Report (see attached). From what I can tell the system is the same as the one found in 'QS/regtest-negf-fft/au111_c6h4s2_gamma_0.50V.inp'. However when I run that job unmodified except to add print commands in the NEGF section (see below) I don't get anything close to what was found in the Technical Report. The job input and output files are attached.

I also have a further question regarding this test. I want to create I-V curves, from what I understand I should therefore use the zero bias transmission coefficients, and set NEGF/CONTACT/ELECTRIC_POTENTIAL to 0 correct?

Any clarity on where I am going wrong would be appreciated. 

   &PRINT
     &DOS
       FILENAME device
       FROM_ENERGY -0.2
       N_GRIDPOINTS 401
       TILL_ENERGY 0.2
     &END DOS
     &TRANSMISSION
       FILENAME transm
       FROM_ENERGY -0.2
       N_GRIDPOINTS 401
       TILL_ENERGY 0.2
     &END TRANSMISSION
   &END PRINT

[Dmitry Ryndyk]

Dear Michael, 

to see the same result, as in the report, you should take zero voltage and other energy limits:

&PRINT
     &DOS
       FILENAME device
       FROM_ENERGY 0.272240982
       N_GRIDPOINTS 401
       TILL_ENERGY 0.492829218

     &END DOS
     &TRANSMISSION
       FILENAME transm

       FROM_ENERGY 0.272240982
       N_GRIDPOINTS 401
       TILL_ENERGY 0.492829218
     &END TRANSMISSION
   &END PRINT

The Fermi level is 0.38253510. The result is in attachment. It is not exactly the same, but it can be for many reasons.  

I am currently revising the NEGF code, and may change the energy levels to be around the Fermi level. If you want to use NEGF, I recommend the latest development version of CP2K. And I will try to answer further questions.  

Concerning your second question. It is the advantage of the NEGF approach that T(E) is changed with bias voltage. But as a simplest way to get I(V), the zero-voltage transmission can sometimes be used. Very carefully to make sense. It depends on the problem, of course. If the energy levels of the central system are not changed at finite voltage, one can omit self-consistency at finite voltage and use T_0(E).

Best wishes,

Dmitry Ryndyk