The energy spectra and optical absorption spectra of isomers Nos. 1, 6, 16 and 46 of fullerene C90 are calculated. Due to the comparison of theoretical and experimental optical absorption spectra, three previously synthesized isomers of C90 fullerene have been identified. The calculations are carried out within the framework of the developed approach, taking into account the intra-node Coulomb interaction of ?-electrons, which plays a crucial role in the formation of the electronic and optical properties of fullerenes. Keywords: fullerene, intra-node Coulomb interaction, Hubbard model, Coulomb integral, energy spectrum, selection rules, optical absorption spectrum.

The energy spectra of ten isomers of trifluoromethyl derivatives of fullerenes C60(CF3)10 and C70(CF3)10 are calculated within the framework of the Hubbard model. Based on the obtained energy spectra, the optical absorption spectra of these compounds are modeled. The calculated optical absorption spectra are compared with the experimental spectra.

Within the framework of Hubbard’s model using an approximation of static fluctuations, the electronic structure and optical properties of compounds of C90 fullerene isomers with chlorine atoms are investigated. The energy spectrum of π electron subsystem is shown to be divided into several unbound electronic subsystems when the number of the attached chlorine atoms becomes greater than (or about) 30. Each of subsystems behaves like a separate system in this case. The energy spectra and optical absorption spectra of ten different chlorine compounds C90@Cln have been calculated. Their optical properties are predicted.

The energy spectra of ten isomers of trifluoromethyl derivatives of fullerenes C 60 (CF 3 ) 10 and C 70 (CF 3 ) 10 are calculated within the framework of the Hubbard model. Based on the obtained energy spectra, the optical absorption spectra of these compounds are modeled. The calculated optical absorption spectra are compared with the experimental spectra. Keywords: trifluoromethyl derivatives, fullerene, Hubbard model, energy spectrum, optical absorption spectrum.

Within the framework of the Hubbard model, the energy spectra of the Cs and C3v isomers of C58 fullerene and dimers based on them are calculated. The obtained curves of the density of electronic states of these systems are compared with the experimental curves of the films, which were obtained by deposition of the Cs and C3v isomers of C58 fullerene on the (1,1,1) gold surface. A comparative analysis of the curves of the density of electronic states shows that in those sites through which a bond is formed between fullerenes, carbon is not in the sp2, but in the sp3 hybridized state.

Within the framework of the Hubbard model, the energy spectra of the C s and C 3v isomers of C 58 fullerene and dimers based on them are calculated. The obtained curves of the density of electronic states of these systems are compared with the experimental curves of the films, which were obtained by deposition of the C s and C 3v isomers of C 58 fullerene on the (1,1,1) gold surface. A comparative analysis of the curves of the density of electronic states shows that in those sites through which a bond is formed between fullerenes, carbon is not in the sp 2 , but in the sp 3 hybridized state. Keywords: fullerene, dimer, energy spectrum, Hubbard model, Hubbard subband, density of electronic states.

The energy spectra and optical absorption spectra of isomers Nos. 1, 6, 16 and 46 of fullerene C90 are calculated. Due to the comparison of theoretical and experimental optical absorption spectra, three previously synthesized isomers of C90 fullerene have been identified. The calculations are carried out within the framework of the developed approach, taking into account the intra-node Coulomb interaction of π-electrons, which plays a crucial role in the formation of the electronic and optical properties of fullerenes.

The article simulates the optical absorption spectra (OAS) of endohedral complexes Er2C2 @ C90 based on isomers No. 44 (C2) No. 21 (C1) of fullerene C90. For this purpose, the energy spectra of the indicated isomers have been calculated. The calculation was carried out within the framework of two models. Within the framework of the first model, which is traditional, only hops of π-electrons from site to site were taken into account (the integral of hopping to the nearest sites B ~ -2.6 eV). Within the framework of the second model, developed in a series of our works [1-5], in addition to hopping from site to site (the integral of hopping to the nearest sites B ~ -1.0 eV), the intrasite Coulomb interaction (ICCI) of π-electrons was also taken into account (the integral of the Coulomb interaction U ~ 7.0 eV). Comparison of the OSS curves obtained by us with the experimental data [5] convincingly indicates that the second model adequately describes the OSS of the endohedral Er2C2 @ C90 complexes based on the investigated isomers. The magnitude of charge transfer from the Er2C2 system to the fullerene shell turned out to be -4e.

Optical absorption spectra (OASs) of endohedral Er2C2@C90 complexes, based on isomers nos. 44 (C2) and 21 (C1) of fullerene C90, have been simulated. To this end, the energy spectra of these isomers have been calculated. The calculations have been performed within two models. Within the first (conventional) model, only hoppings of π electrons between sites (nearest-neighbor hopping integral B ~ –2.6 eV) has been taken into account. Within the second model, intrasite Coulomb interaction (ISCI) of π electrons (Coulomb-interaction integral U ~ 7.0 eV) has been also taken into account along with intersite hoppings (nearest-neighbor hopping integral B ~ –1.0 eV). Comparison of the obtained OAS curves with the experimental data c-onvincingly indicates that the second model describes adequately the OASs of endohedral Er2C2@C90 complexes, based on the isomers under investigation. Charge transfer from the Er2C2 system to the fullerene shell was –4e.