QuantumATK > General Questions and Answers

Electrode material in DeviceConfiguration

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pippin:
A real-world device almost always has metal electrode.  But if I am just interested in bulk transport, can I set my electrode material in DeviceConfiguration to be the same as my bulk material?  Or, must I have some kind of metal material for my electrodes?

Nordland:
Your electrode can be anything. Even a semiconductor.

In VNL 2010.02 there is a custom builder for setting up an "ideal bulk" device configuration, which is perfect for understanding transport properties of a bulk material.

Anders Blom:
Do note, however, that converging a system with semiconducting electrodes might be harder.

Also, people often try "the simplest thing imaginable", which might be a perfect 1D chain of metal atoms, for instance. This has a very simple analytic solution (transmission T(E)=the number of bands crossing energy E), but for various reasons it's not a very simple system to compute using ATK, esp. at finite bias. Essentially, the ATK algorithms are designed to work best when there is a clearly defined place in the structure for the applied bias voltage to drop, i.e. there should be some resistance.

This is particularly noticeable for 3D systems, if one tries to compute the transmission spectrum of bulk gold, for instance. In fact, "conductance" in the Landauer picture (which is what ATK calculates) is not a well-defined quantity for a macroscopic bulk conductor, but rather it applies to some "quantum point contact", which should be understood in a broad sense but still clearly is related to microscopic (or nanoscopic) geometrical features.

pippin:
O.K.  Suppose that the calculation with two semiconductor electrodes managed to converge.  Also, suppose that the subsequent transmission calculations also converged.  Are the resulting I-V (or conductance) characteristics not very well defined?  I guess I am a bit confused.  Could you clarify what I can and cannot draw from these transmission calculations if I have semiconductor (or insulator) electrodes as opposed to metal electrodes?  Thanks!

 

Nordland:
There are no difference between metallic electrodes and semi-conducting electrodes in the terms of how to understand and perform the analysis for your result.

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