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Competition between Hückel's Rule and Jahn-Teller Distortion in Small Carbon Rings: A Quantum Monte Carlo Study
Iuegyun Hong1, Jeonghwan Ahn1, Hyeondeok Shin2
1Department of Physics, Konkuk University, Seoul 05029, Korea.
Abstract:
Structural properties and energetics of carbon rings are studied with the diffusion Monte Carlo (DMC) method. Our DMC-based geometry optimization reveals that both polyynic C4 and cumulenic C4 rings exhibit bond length alternations for n ≥ 3, which is understood to be due to Jahn-Teller distortions. The bond length alternation even in a cumulenic (4n + 2) carbon ring was experimentally observed in a recently synthesized C18 molecule. From a comparison of the DMC cohesive energies of C4 with those of C4, we present a comprehensive picture of the competition between Hückel's rule and Jahn-Teller distortion in small carbon rings; the former is more dominant than the latter for n < 5 where C4 rings are more stable than C4, while C4 rings are as stable as C4 for n < 5 where dimerization effects due to Jahn-Teller distortion are more important.
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