Periodic Boundary Condition and Understanding Normalizing

[ruyam]

Dear Anders Sir,

The reason I wanted to know about the energy band diagram for an infinite graphene sheet(as you rightly said in the posthttp://quantumwise.com/forum/index.php?topic=1551.15#.VLZyZh2xr7B) was to verify about periodic boundary condition due to some discrepancy I found by looking at the band-gap. I found the following contradiction which made me do the exercise:

When I change the width and do transport calculations keeping periodic boundary condition I expected that the current increases in the same ratio as the width. But what I found that this trend did not follow. I fail to understand that if I have periodic boundary condition then the current/width ratio(i.e. the normalized current value) should had been constant. Please help me understand what am I missing in here.

PFA the python files.

[ruyam]

pls reply!

[Anders Blom]

Whether it is constant or not may depend a lot on the accuracy of your calculation, e.g. if you have enough k-points. But since you didn't show the results it's hard to judge "how non-constant" it is, and thus if it's reasonable or not. But yes, you would expect it to be constant.

That said, a perfect system is hard to compute at finite bias (this question seems to pop up every week here on the Forum), so there may be some influence of that too.