[DFTB-Plus-User] DFTB+NEGF: Dangling bonds in a graphene nanoribbon

[anz118466 at cse.iitd.ac.in]

Hi all,

I have tried performing transport calculations of a graphene nanoribbon
using the DFTB+NEGF package. As testcases, I took two scenarios: one, a
GNR with the edge dangling bonds left intact and second, a GNR with H
atoms attached to the edges. In both
http://www.dftb-plus.info/pipermail/dftb-plus-user/2012/000816.htmlthe
cases, I took an equal number of C atoms.

As per the thread given on
http://www.dftb-plus.info/pipermail/dftb-plus-user/2012/000816.html, DFTB
does not specially treat dangling bonds. Yet, in my two testcases, SCC
convergence is achieved in approx. 20 cycles in the second case (with H
atoms) , and is not achieved at all in the first case (without H atoms)
even after 500 cycles. Is this expected? Do the dangling bonds make this
much of a difference?

Thanks and Regards,
Anusha Iyer