ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Finite-field technique has been applied to the calculation of π molecular polarizabilities within the Pariser–Parr–Pople Hamiltonian. This formalism allows to analyze large oligomers containing up to 400 atoms, and asymptotic behaviors may be attained in some cases. We have investigated the role of the polymer size, the backbone geometries, the presence of neutral and charged defects (solitons, polarons, bipolarons), the chemical nature of the monomeric unit on the polarizabilities. Generally, the polarizabilities are not deeply modified by a change of the geometrical characteristics, and may lead to huge values for sufficiently large chains. Besides, the charge of the system is the leading factor which determines the values of this property. The evolution of the polarizability with the number N of π atomic centers, αu depends largely on the charge, and on the defect. For the neutral systems, the polarizability per monomeric unit αu increases smoothly, and then exhibits an asymptotic behavior with N. For polymers with a defect, this variation is different: αu first increases with N, reaches a maximum αu max for Nmax, and finally tends to an asymptotic value. The values of αu max for Nmax depend on the type of defect (soliton vs polaron) and are rather sensitive to the dependence of the first-neighbor one-electron interaction with the interatomic distance. A large number of results on polyacetylene and polyheterocycles shows that there exists a simple law between the polarizability and the electronic gap, independently of the type of the monomeric unit. But this relation shows a deviation from a simple proportionality behavior, as soon as α reaches large values (as for example in polymers with defects).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.462486
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