[Pw_forum] Defining an antiferromagnetic graphene nanoribbon

[Nicola Marzari]

Thanks Stefano for the feedback on the different issues !

On the first part (sp3 and sp2+pz having the same number of
effective electrons in the p and s channels) I would tend to agree -
but it would be indeed nice to do an experiment with a carbon atom
having occupation numbers 2 2/3 2/3 2/3, and 1 1 1 1 for
the 4 levels (2s and 2p) - energy as a function of cutoff.
The second case should be closer to diamond and graphite/graphene
than the first. Any takers ?

On the second part, I'm a bit more puzzled. I agree that
discontinuities in the E-vs-V curve appear, especially for
sparse k-point sampling, due to the sudden increase in
the number plane waves when the cutoff crosses some critical
value. Still, those discontinuities would always appear as a
sudden drop in total energy, since the basis of plane waves has
discontinuously become larger.
http://www.pwscf.org/pseudo/1.3/UPF/C.pbe-rrkjus-test-diamond.pdf
looked a bit different - hence my puzzlement. I though at augmentation
charges and the existence of fourier oscillations outside the core
region, due to the multipole representation of the charge, but
not sure why it would be more relevant in diamond (where the C-C
distance is longer)

			nicola

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Prof Nicola Marzari   Department of Materials Science and Engineering
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