Inconsistant transmission between bulk and bulk-like device

[kaihuang]

I'm calculating the transmission of a 2D material.

I tried two approaches:

1. Transmission of the bulk in the unit cell.
2. Transmission of the bulk-like device, where the left electrode, right electrode, and central area are all the same unit cell structure.

I assumed the transmission results would be identical. However, the results are different:

[image in the attachment]

(image link in case it doesn't show: https://imgur.com/wRPUPpw)

The left image shows the unit cell transmission, while the right image shows the bulk-like device transmission. Both calculations use GGA with polar spin and no SOC included.

You can observe that the transmission curves relative to the Fermi energy are different, with the transmission from the unit cell being larger.

My question is, why could this difference occur? Should the results be the same, and which one should be considered correct?

Thanks,
Kai

[Anders Blom]

They should be the same, but can be affected by numerical convergence (they do look similar, so I think that is the case). Maybe you have different k-point settings or maybe the device needs to be better converged. 4 units is also perhaps a bit small for the center part, depending on the size in C of the unit cell.