Abstract:The magnetic properties of a class of 1-D -systems having a frontier Ž . half-filled band of degenerate MOs localized within the elementary units EU were studied theoretically. The localization of the MOs is caused by the symmetry of the -fragments which form the EUs. The localization and non-overlapping of the MOs Ž . results in vanishing of the direct Hund and the kinetic exchange interaction between Ž the unpaired electrons. The indirect exchange of the unpaired electrons spin-polarization . exchange occurs… Show more
“…The ground state of hydrocarbon NK is a high-spin triplet. Using the four-electron four MOs CI scheme (see ref ) for the singlet−triplet splitting Δ E ST = E S − E T , one obtains for hydrocarbon NK a value on the order of magnitude of 0.1 eV. …”
Section: Numerical Results and Discussionmentioning
The energy spectra of three classes of polybenzenoid hydrocarbons with a large number N (N ≈ 10 3 ) of carbon atoms have been studied theoretically. It is shown that in the asymptotic case N f ∞ the energy gap (EG) ∆E(Nf∞) is different from zero if the electron correlation is taken into account; that is, the π systems calculated should possess semiconductor properties. The results for the ∆E(Nf∞) * 0 of the hydrocarbons are in qualitative agreement with the results calculated for the EG of three classes of 1-D ladder polymers, which can be considered as models of quasi-1-D graphite. With increasing width (L) of the polymers, the band gap ∆E(Lf∞) approaches a value different from zero. The problem of the existence of defect states of hydrocarbons with vacancies is briefly discussed.
“…The ground state of hydrocarbon NK is a high-spin triplet. Using the four-electron four MOs CI scheme (see ref ) for the singlet−triplet splitting Δ E ST = E S − E T , one obtains for hydrocarbon NK a value on the order of magnitude of 0.1 eV. …”
Section: Numerical Results and Discussionmentioning
The energy spectra of three classes of polybenzenoid hydrocarbons with a large number N (N ≈ 10 3 ) of carbon atoms have been studied theoretically. It is shown that in the asymptotic case N f ∞ the energy gap (EG) ∆E(Nf∞) is different from zero if the electron correlation is taken into account; that is, the π systems calculated should possess semiconductor properties. The results for the ∆E(Nf∞) * 0 of the hydrocarbons are in qualitative agreement with the results calculated for the EG of three classes of 1-D ladder polymers, which can be considered as models of quasi-1-D graphite. With increasing width (L) of the polymers, the band gap ∆E(Lf∞) approaches a value different from zero. The problem of the existence of defect states of hydrocarbons with vacancies is briefly discussed.
“…The term J ind expresses the indirect exchange caused by the spin polarization within the conjugated π‐electron system. This term can be calculated using formalism described earlier 17, 18. The sign of J ind is determined by the structure of the EU, the symmetry of the SOMOs and the interaction between the units.…”
ABSTRACT:The character and the magnitude of magnetic interaction in 1-D stacks of mixed molecular radical crystals (MMRCs) and mixed molecular ion radical crystals (MMIRCs) of alternant aromatic hydrocarbons have already been studied theoretically. In this work nonalternant 1-D stacks built of -electronic subunits are considered. Some of the elementary units are singly or doubly charged (MMIRCs), others are neutral (MMRCs); alternant and nonalternant subunits are used as building blocks. Qualitative investigations based on the band theory of exchange effects in solid organic open-shell systems are carried out. The contributions to the effective exchange integral J eff : direct (Hund's), kinetic and indirect, are calculated. Structures of 1:1 MMRCs and MMIRCs with positive value of the integral J eff , accounting for the spin exchange of the electrons in the half-filled band, i.e., with ferromagnetic ground state, are suggested. The influence of different parameters (molecular size, presence of heteroatoms, localization versus delocalization, alternant versus nonalternant, charge, etc.) on the magnitude of the net exchange is discussed.
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