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Recent work found that soldering CdTe quantum dots together with a molecular CdTe polymer yielded field-effect transistors with much greater electron mobility than quantum dots alone. We present a computational study of the CdTe polymer using the active-space variational two-electron reduced density matrix (2-RDM) method. While analogous complete active-space self-consistent field (CASSCF) methods scale exponentially with the number of active orbitals, the active-space variational 2-RDM method exhibits polynomial scaling. A CASSCF calculation using the (48o,64e) active space studied in this paper requires 1024 determinants and is therefore intractable, while the variational 2-RDM method in the same active space requires only 2.1 x 107 variables. Natural orbitals, natural-orbital occupations, charge gaps, and Mulliken charges are reported as a function of polymer length. The polymer, we find, is strongly correlated, despite possessing a simple sp³-hybridized bonding scheme. Calculations reveal the formation of a nearly saturated valence band as the polymer grows and a charge gap that decreases sharply with polymer length. [ABSTRACT FROM AUTHOR]

Strongelectron correlation within a quasi-spin model of chromophoreswas recently shown to enhance exciton energy transfer significantly.Here we investigate how the modulation of the electronic structureof the chromophores by chemical substitution can enhance energy-transferefficiency. Unlike previous work that does not consider the directeffect of the electronic structure on exciton dynamics, we add chemicalsubstituents to the fluorone dimer to study the effect of electron-donatingand electron-withdrawing substituents on exciton energy transfer.The exciton dynamics are studied from the solution of a quantum Liouvilleequation for an open system whose model Hamiltonian is derived fromexcited-state electronic structure calculations. Both van der Waalsenergies and coupling energies, arising from the Hellmann–Feynmanforce generated upon transferring the dimers from infinity to a finiteseparation, are built into the model Hamiltonian. Though these twoeffects are implicitly treated in dipole-based models, their explicitand separate treatment as discussed here is critical to forging thecorrect connection with the electronic structure calculations. Wefind that the addition of electron-donating substituents to the fluoronesystem results in an increase in exciton-transfer rates by factorsranging from 1.3–1.9. The computed oscillator strength is consistentwith the recent experimental results on a larger heterodimer systemcontaining fluorone. The oscillator strength increases with the additionof electron-donating substituents. Our results indicate that the studyof chromophore networks via electronic structure will help in thefuture design of efficient synthetic light-harvesting systems. [ABSTRACT FROM AUTHOR]