Conductivity in polyacetylene. II. Ab initio and tight-binding calculations of soliton structure and reorganization energy in ordered and disordered structures

Abstract

Alkali-doped polyacetylene is considered as an electron-transfer system. To estimate the reorganization energy due to bond-length changes when electrons are added or subtracted, we applied the (U)MP2 and CASSCF methods to small systems of the type H(CH), H. The simple tight-binding (Hiickel) model with bond-length-dependent resonance integrals has been applied to the same and larger polyenes. The bond lengths are obtained via the bond orders for the various oxidation states. The results agree very well with the ab initio results and experiments for small polyenes. Odd-N and even-N systems behave differently. In odd-N systems, a structural "soliton" exists in the neutral molecule. An electron can be added or removed without bond-length change. In even-N chains, with perfect bond alternation in the neutral molecule, the bond length changes when an electron is accepted occur over about 20 carbon atoms. The reorganization energy tends to a constant value (0.22 eV) as the chain length is increased. Soliton structure is studied as a function of out-of-plane torsional defects and it is found that an additional electron is localized primarily on a segment with an odd number of carbon atoms. In the presence of positively charged ions, electrons are attracted toward this charge and positive solitons formed at some distance from the perturbing ion. 0 1996

Conductivity in polyacetylene. VI. Semiconductor—Metal transition of alkali‐doped polymer

“…In the low-doping region, there seems to be general agreement that the electrons go to already existing solitons and create spinless charged solitons. This is consistent with w x our previous results 28, 29 . The solitons have the highest electron affinity and therefore first receive electrons at doping.…”

On the calculation of the spectrum of large Hückel matrices, representing carbon nanotubes, using fast Hadamard and symplectic transforms

“…It follows that the calculation of MO results for this kind of molecular system requires the use of efficient diagonalization algorithms. The present study is devoted to the exploration of new diagonalization methodologies capable of obtaining the energy spectrum of large un-localized carbon systems to the Hu¨ckel level [12][13][14][15].…”

Electron transport through polyene junctions in between carbon nanotubes: An ab initio realization

“…With the fitted hopping energy t ¼ 2:458 eV being used, the TB results are shown in the range À0:4t < E < 0:4t, which corresponds to the range À1:0 eV < E < 1:0 eV in the ab initio results. the electronic structure studies of polyene radicals [29][30][31] show that the HOMO of isolated all-trans C 11 H 13 is around À8 eV, which implies an even deeper HOMO of isolated C 7 H 9 . Therefore, when the polyenes link the electrodes, charge transfer is expected.…”