Negative zero bias conductance

[huckelbuckel]

I am calculating zero bias conductances (ZBC) for narrow width twisted armchair graphene nanoribbons. For 3-AGNR and 5-AGNR (width) i am getting low but positive values..something like 10^-18 and 10^-9 Siemens respectively.... but for 4-AGNR (width) these values are low and NEGATIVE.

Why i am getting negative zero bias conductance?? Is it possible? I have kept same conditions for calculations of all three 'width' cases. Do i need to increase the (+E,-E) energy window of transmission. Right now it is (+2eV -2eV)  See attached screenshot of transmission and 'negative' value of ZBC..

[Anders Blom]

Well, it's negative, but it's also so close to zero that it doesn't matter, it's just due to numerical noise. The correct value for the low-bias conductivity is zero - you need to apply a substantial bias to bridge the band gap of an AGNR.

[huckelbuckel]

thanks for this clarification