Can I run this command using VNL?

[lknife]

In tutorial "Modeling metal–semiconductor contacts: The Ag–Si interface", in section "Silicon doping and depletion layer length", there is no bias parameter set for the HartreeDifferencePotential calculation.

It was said in the tutorial that "The wiggles of the potential can make it hard to see if it has converged to the electrode value. ". That means, the potential could be converged to the electrode value. However, the two figures in this section are different. The obvious difference lies on the ending values (converging value) of the HartreeDifferencePotential at the two electrodes. For example, it ends at about 3eV at the right electrode in the first figure, while it ends at about 0eV in the second figure. Assuming the parameter settings (such as bias) for the calculations were the same, where did the inconsistence come from?

Can anyone tell me the meaning of the Y coordinate and help me with this problem?

[Petr Khomyakov]

There is no bias voltage applied in this calculation. However, the Hartree Difference Potential (HDP) does not need to be the same in the left and right electrodes at zero bias. The definition of the HDP is discussed in Notes at http://docs.quantumwise.com/manuals/Types/HartreeDifferencePotential/HartreeDifferencePotential.html.

The second figure shows the same HDP that has been averaged along the Z-direction to smoothen the oscillation related to the discrete nature of atoms. The plot is rigidly shifted as you have noticed, but as any electrostatic potential the HDP is defined up to a constant. So, it is equally good for describing band bending in Si discussed in the tutorial, and was set to zero in the right electrode to align the averaged HDP with the Fermi level in the doped Si (comprising the right electrode) as shown in the PLDOS figure. 

[lknife]

Thank you very much for you help!

You mean that the EDP or HDP does not need to be the same in the left and right electrodes at zero bias, but in my case, there was a bias of 0.1V between the two electrodes, what would it be then? I am now running another calculation for the EDP without bias and want to compare the results with and without bias. I have the question: what's the meaning of the difference in the EDP or HDP curve between the left and right electrodes, just representing the band bending near the interface?

[Petr Khomyakov]

what's the meaning of the difference in the EDP or HDP curve between the left and right electrodes, just representing the band bending near the interface?

The macroscopically-averaged HDP shows the band bending far from the interface, and it reaches constant values in the left and right electrodes. Note that band bending is not defined at the interface, as its definition relies on the Thomas-Fermi approximation that is not valid at or sometime even near the interface.

One may use the HDP curve together with the PLDOS graph to understand band alignment between two dissimilar semiconductor structures.