Stability of the high-spin ground state in alternant π-conjugated organic molecules

Sinha, Bhabadyuti ; Albert, I. D. L. ; Ramasesha, S. (1990) Stability of the high-spin ground state in alternant π-conjugated organic molecules Physical Review B: Condensed Matter and Materials Physics, 42 (14). pp. 9088-9097. ISSN 1098-0121

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Alternant quantum cell models with unequal numbers of atoms on the two sublattices have been predicted to have a high-spin ground state. In this paper, we examine the stability of this high-spin ground state with respect to breaking the alternancy symmetry and distortion of the backbone conjugation. We find that in the Pariser-Parr-Pople (PPP) models and the Hubbard models with weak correlations, the ground state continues to be the high-spin state, even when alternancy symmetry is broken by introducing large site-energy differences. In the Hubbard model, for strong correlation strengths, the ground state switches from a high-spin to a low-spin state when large site-energy differences are introduced. The bond-order calculations in all these models shows that the low-spin state is susceptible to dimerization of the backbone. In the distorted chains, the low-spin state stabilizes to a greater extent leading to low-spin ground states at least in "soft" lattices. However, experience with one-dimensional systems suggests that the lattice distortion could occur unconditionally leading to low-spin ground state in infinitely long polymers. Thus, realization of organic ferromagnetics via high-spin polymers could be elusive.

Item Type:Article
Source:Copyright of this article belongs to The American Physical Society.
ID Code:39446
Deposited On:12 May 2011 14:15
Last Modified:12 May 2011 14:15

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