Electronic Structure and Optical Absorption of Fullerenes as Strongly Correlated Systems by the Example of Molecule C 96
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TROSCOPY AND PHYSICS OF ATOMS AND MOLECULES
Electronic Structure and Optical Absorption of Fullerenes as Strongly Correlated Systems by the Example of Molecule C96 (C2) A. I. Murzasheva, *, M. Yu. Kokurina, and S. K. Paimerova a Mari
State University, Yoshkar-Ola, 424001 Russia *e-mail: [email protected]
Received February 10, 2020; revised April 10, 2020; accepted May 4, 2020
Abstract—The energy spectrum of isomer no. 181 (C2) of fullerene C96 is calculated within the approximation of static fluctuations taking into account the intrasite Coulomb interaction with parameter U ~ 10 eV, and its optical absorption spectrum is modeled based on the calculated energy spectrum. The obtained optical absorption spectrum is in a good qualitative agreement with the experimental curve. A similar curve obtained within a conventional model with the intrasite Coulomb interaction disregarded differs significantly from the experimental curve. Keywords: fullerene, energy spectrum, optical absorption spectrum, π electron, Hubbard subband, optical transitions DOI: 10.1134/S0030400X20090143
INTRODUCTION In the recent years, much interest of both theoreticians and experimenters has been shown in fullerenes and similar carbon structures because of, on the one hand, promising applications of these compounds in various branches of production, instrument engineering, and medicine and, on the one hand, the remaining deficiencies and uncertainties in the theory of their electronic structure. The electronic structure of fullerenes is determined by the fact that carbon in these systems (as in graphite, carbon nanotubes (CNTs), and graphene) is in the sp2-hybridized state. Three out of four carbon valence electrons are bound by rigid bonds (σ bonds), which form the system framework, while the fourth-electron states form the so-called π band with partially localized electrons. Thus, almost all observed properties (in particular, electrical conductivity and optical absorption) are determined by the states of these electrons. The basic studies devoted to the electronic structure of the systems under consideration are those by Wallace [1] and Sagawa [2]. Wallace showed in 1948 [1] within the Hueckel approximation that π electrons form a conduction band with a width of 6B in the graphite plane, where B is the hopping integral of π electrons between neighboring sites. In [2], the density of electron states in graphite was measured by Auger spectroscopy. The results obtained suggest that the filled part of the conduction band (a half of the conduction band in this case) had a width of ~5.8 eV. Based on this value, the hopping integral was estimated to be B ≈ –2 eV. The later studies [3–5] devoted
to the optical absorption of CNTs yielded a close value (B ≈ –2.6 eV). The optical absorption spectra (OASs) of fullerene C60 were explained based on the energy spectrum obtained at this value of parameter B. However, attempts to explain OASs for other fullerenes within the simple Hueckel model with parameter B ≈ –2.6 eV did not yield clear and unambiguous
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