Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Parity law of the singlet-triplet gap in graphitic ribbons   This work explores the possibility to transfer the parity law of the
singlet-triplet gap established for square ladders (gapped for even number of
legs, gapless for odd number of legs) to fused polyacenic 1-D systems, i.e.,
graphite ribbons. Qualitative arguments are presented in favor of a gapped
character when the number $n\_{\omega}$ of benzene rings along the ribbon width
is odd. A series of numerical calculations (quantitative mapping on spin 1/2
chains, renormalized excitonic treatments and Quantum Monte Carlo) confirm the
parity law and the gapless character of the ribbon for even $n\_{\omega}$.

21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
2
The categories of this paper are: math
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio