Correlation in polymers

More General Treatments of Electron Correlation in Polymers.—The introduction of excitonic states was just a simple example to show how one can go beyond the HF approximation to obtain correlated electron-hole pairs, whose energy level(s) may fall into the forbidden gaps in HF theory, and form the basis for interpretation of optical phenomena in semiconducting polymers. The schemes described until now for investigation of certain types of correlation effects (the DODS method for ground-state properties and the exciton-picture for excited states) are relatively simple from both the conceptual and computational points of view and they have been actually used at the ab initio level. It is evident, on the other hand, that further efforts are needed in polymer electronic structure calculations if we want to reach the level of sophistication in correlation studies on polymers which is quite general nowadays in molecular quantum mechanics. 

On the larger length scale, correlations in polymer density fluctuations are described by eqn [42] and consequently, Lorentzian angular distribution of scattered radiation applies ... 

Mendelsohn AS, Delacruz MO, Torkelson JM (1993) Correlations in polymer melts and solutions as investigated by fluorescence nonradiative energy-transfer—a novel comparison of theory to experiment by fluorescaice intensity decay measinements. Macromolecules 26 (25) 6789-6799. doi 10.1021/ma00077a015... 

Narasimachary, S. R, Roudgar, A., and Eikerling, M. H. 2008. Ab initio study of interfacial correlations in polymer electrolyte membranes for fuel cells at low hydration. 

The treatment of correlation, even in periodic polymers, presents a formidable and as yet only partially solved problem if the unit cell is large. This problem is examined by initially discussing localization techniques in larger molecules, and then presenting the first results of the application of localized orbitals for correlation calculations using many-body perturbation theory and the coupled-cluster approach. It is also shown how localization of the orbitals within a large unit cell can be applied for correlation calculations if this unit cell is repeated in a periodic way in the polymer. This chapter also deals with the correlation in polymers with smaller unit cells (like polyacetylene, polydiacetylene, and polyethylene) and includes a detailed discussion of the results obtained. Finally, some ideas about possibilities of treating correlation in disordered chains are noted. 

Sec. 5.5 Correlation in Polymers with Large Unit Cells... 

CORRELATION IN POLYMERS WITH LARGE UNIT CELLS... 

---