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.
