  The structures, cohesive energies and HOMO-LUMO gaps of graphene nanoflakes
and corresponding polycyclic aromatic hydrocarbons for a large variety of size
and topology are investigated at the density functional based tight-binding
level. Polyacene-like and honeycomb-like graphene nanoflakes were chosen as the
topological limit structures. The influence of unsaturated edge atoms and
dangling bonds on the stability is discussed. Our survey shows a linear trend
for the cohesive energy as function of Ns/N (N - total number of atoms and Ns
is number of edge atoms). For the HOMO-LUMO gap the trends are more complex and
include also the topology of the edges.
