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We have performed DFT calculations, within a pseudopotential
total-energy scheme for periodic systems [36].
We use the local-density approximation (LDA)
[37,38] for the exchange-correlation energy,
Troullier-Martins pseudopotentials [39]
for boron, carbon and
nitrogen and a modified Kerker pseudopotential [40]
for hydrogen,
and a plane-wave
basis-set for the
wavefunction
expansion up to a kinetic energy
cutoff of 60 Ry. The polymers were modelled in a periodic cell with a
large distance
between neighbouring chains to minimize
their interaction. The Brillouin zone was sampled using twenty
-points.
Both the atomic
coordinates and the cell degrees of freedom were
fully relaxed.

Peter D. Haynes
2002-10-28