QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: Jenny on October 19, 2016, 17:56
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Hello, everyone.
I found that in the tutorials (http://quantumwise.com/support/tutorials/item/515-isotope-impurity-effect-on-a-single-wall-carbon-nanotube), the electron transmission spectrum has a dip at the Fermi level for carbon nanotube (6,0). However, theoretically the transmission value should be 2, instead of 0.
what is the problem with the tutorial? And how can we get the correct result?
Jenny
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Why should it be 2? A (6,0) tube has a small band gap.
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Why should it be 2? A (6,0) tube has a small band gap.
Hi, Dr. Blom.
According to the reference http://pubs.acs.org/doi/pdf/10.1021/jz100889u (Definitive Band Gaps for Single-Wall Carbon Nanotubes). They used B3LYP and found that the band gap for CNT(6,0) is 0. So I assume that the transmission spectrum would have no gap as well. Though no experimental data or LDA approximation calculation for CNT (6,0) mentioned here.
Thanks.
Jenny
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ATK doesn't use B3LYP, so that explains the difference. Indeed, there is no experimental confirmation of the metallic nature of (6,0), or rather there wasn't in 2010 when that paper was written. To be honest I find the band structure of the (6,0) structure in Fig. 2a suspicious - I can except a small gap appears for some model and another gives metallic, but overlapping conduction and valence bands like that is unusual (it's sometimes called negative band gap) and I wonder if maybe it's a spurious result. At least it should have been explored in more detail in the paper. I respect the authors, but that figure look weird, and their argument of why tight-binding gives a different result is not convincing since LDA would capture the curvature too, and they don't explain that difference.