Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Higher energy triplet-pair states in polyenes and their role in
  intramolecular singlet fission   Probing extended polyene systems with energy in excess of the bright state
($1^1B_u^+$/$S_2$) band edge generates triplets via singlet fission. This
process is not thought to involve the $2^1A_g^-$/$S_1$ state, suggesting that
other states play a role. Using density matrix renormalisation group (DMRG)
calculations of the Pariser-Parr-Pople-Peierls Hamiltonian, we investigate
candidate states that could be involved in singlet fission. We find that the
relaxed $1^1B_u^-$, and $3^1A_g^-$ singlet states and $1^5A_g^-$ quintet state
lie below the $S_2$ state. The $1^1B_u^-$, $3^1A_g^-$ and $1^5A_g^-$ states are
all thought to have triplet-triplet character, which is confirmed by our
calculations of bond dimerization, spin-spin correlation and wavefunction
overlap with products of triplet states. We thus show that there is a family of
singlet excitations(i.e., $2^1A_g^-$, $1^1B_u^-$, $3^1A_g^-$, $\cdots$),
composed of both triplet-pair and electron-hole character, which are
fundamentally the same excitation, but have different center-of-mass energies.
The lowest energy member of this family, the $2^1A_g^-$ state, cannot undergo
singlet fission. But higher energy members (e.g., the $3^1A_g^-$) state, owing
to their increased kinetic energy and reduced electron-lattice relaxation, can
undergo singlet fission for certain chain lengths.

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The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat