Do I need to relax the interface before constructing the device?

[lknife]

Dear all,

I am studying the interface based devices following the tutorial "Modeling metal–semiconductor contacts: The Ag–Si interface". I have two questions on this topic, expecting your kind help!

(1) After constructing the interface using "Interface" plugin, such as a in-plane MoS2-WSe2 interface (seen in the attached file), can I use a smaller unit cell (about 2nm) to represent the interface-based device instead of constructing a full-length device (such as 5nm or longer)? That is, I want to use this smaller unit cell for geometry optimization in order to save time. After that, I can construct the full-length device configuration by increasing the size of the central region at the interface of the respective electrode. Is it reasonable?

(2)  After relaxation of the unit cell, I want to construct a device using "device from bulk" plugin. Do I need to relax the electrode and central region, as well as the whole device configuration again according to the tutorial? Or just use the device obtained from "device from bulk" for further calculation?

Thank you very much for your time and kind help!

[Petr Khomyakov]

Regarding #1, you can definitely do it in the way you have described it. In fact, it would be wise to do it, even if you want to optimize the device structure built in step 2.

Regarding #2, you cannot optimize the electrodes and electrode extensions for device configuration, i.e., when the device is already built; you should have done it in step 1. You may still do geometry optimization for the central region or its part if you expect significant structural reconstruction in the central region of the device.

 

[lknife]

Thank you very much for your kind reply!

Since I am following the tutorial "Modeling metal–semiconductor contacts: the Ag–Si interface", after constructing the device configuration, the tutorial did the geometry optimization of the electrode and central region by splitting the device into three different parts.

What I want to know is:
If I have finished optimizing the geometry of the interface configuration using a smaller unit cell, when I build the device configuration from the unit cell (bulk), do I need to relax the device again in the way as described above? or just use the device configuration for further calculation?

Thank you again for your help!

[Petr Khomyakov]

If you have properly relaxed the bilayer structure before building the device from bulk, you would not really need to relax the electrodes.

[lknife]

Thank you very much for your reply! It's really helpful!