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Quantum and Classical Studies of Calcium and Zinc Clusters and of Pyrrole Oligomers

Show simple item record Dai, Yafei
dc.creator Dai, Yafei 2009-01-12 2009-02-12T21:12:46Z NO_RESTRICTION en 2009-02-12T21:12:46Z 2009-02-12T21:12:46Z
dc.description.abstract An all electron hybrid density functional approach (DFT) with very large basis sets was used for studying Ca(2) through Ca(19) and Zn(3) through Zn(11) neutral clusters and their cluster anions. Energetics, structure and vibrational analysis of all these neutral clusters and cluster anions are reported. The calculated electron affinities (EA) are in excellent agreement with experiment. Additionally, the electron detachment binding energies (BE) up to Ca(6^-) and Zn(6^-) were identified by analyzing the ground and excited states of the cluster anions and of their corresponding neutral clusters. The theoretical BE is in very good agreement with experiment for both calcium and zinc cluster anions. Polypyrrole (PPy) is a conjugated polymer prototype of conducting polymers. The energetically preferred spatial conformation and charge distribution of n-Py oligomers (n = 1 - 24) in both the reduced and oxidized phases are obtained and analyzed in this work within the hybrid density functional theory. Binding energies, HOMO-LUMO gap energies, radius of gyration, end-to-end distance and vibrational frequencies are reported as a function of oligomer length. The band structure of infinite PPy gives a band gap energy in excellent agreement with experiment for reduced PPy. Evolution of the band gap and the charge-localized states as a function of PPy oxidation level is reported. Based on the DFT results of n-Py oligomers, a classical potential model to treat dense systems of PPy is developed within a modified rigid-ion polarizable force field. This model potential is then used in the Adaptive Tempering Monte Carlo and the Metropolis Monte Carlo simulations of a 192 4-Py system and 64 12-Py system at different densities. The energy, end to end distance, radius of gyration and order parameter as a function of density are inspected. It is shown that these systems have the structural characteristics of liquids. However, the calculations show that as the density is increased, the system develops regions of stacked chains.
dc.language.iso en_US en
dc.subject Calcium Cluster en_US
dc.subject Pyrrole Oligomer en_US
dc.subject Monte Carlo en_US
dc.subject Zinc Cluster en_US
dc.subject Density Functional Theory en_US
dc.subject Electron Detachment Spectra en_US
dc.title Quantum and Classical Studies of Calcium and Zinc Clusters and of Pyrrole Oligomers en
dc.type Dissertation en Doctor of Philosophy in Computational Sciences and Informatics en Doctoral en Computational Sciences and Informatics en George Mason University en

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