ИСТИНА

Low-lying electronic terms of hydrocarbons [С 7]q (q=3,5) were calculated within complete active space self-consistent field (CASSCF) under the external axial electric field. Systems [С7]q are a finite fragments of zigzag carbon nanotubes (7,0) containing q cyclacene rings with hydrogen atoms added for filling free valences of carbon atoms having D7h point group symmetry. Such systems have a specific set of one-electron states (edge states), characterized by exponential damping along cylinder axis. These states are localized near the bases of cylinder and they lie near Fermi level. There are four such states for systems [С7]q (q=3,5)(e” 3 e’3) that with four electrons were included in active space of CASSCF method in accordance with our previous work [1]. In the absence of field ground state of [С7]q is open-shell singlet, next stages are triplet and quintet. All these states are very close in energy, forming first tier of states, and can be interpreted as interaction of electrons with opposite spins localized at the opposite bases of nanotubes cylinder. The energy splittings within first tier are well described by Heisenberg Hamiltonian. One-electron edge states under the electric field were described in article [2]. Systems with such states under electric field were theoretically found to posses the half-metallicity properties, that means electrons with one spin flavor have zero electronic energy gap, and nonzero for other. The behavior of many electron states under the influence of axial electric field were considered in current work. Two main regions electric field distinguishing by systematic of low-lying levels were observed. Let us call them “low field” and “high field”. Under the influence of “low field” (E<0.02a.u.) the low lying many-energy levels structure is analogous to the structure without field. Only Heisenberg splittings within first tier are weakly disturbed. Under the influence of “High field” low lying electronic structure are crucially changed. The lowest state became closed-shell singlet. These dramatic changes are due to jump of electrons under electric field from one base of cylinder to another. The energy distance from the ground singlet state to the lowest triplet and quintet states are considerably increased. In other words free radical character of zigzag carbon nanotubes in “high field” disappears. This work was supported by RFBR (grant № 10-03-00665). Pavlov M., Ermilov A. // Int. J. Quantum Chem. 2011. V. 111. P. 2592 Mananes A., Duque F. // Phys Rev B. V. 78. P. 35432