Article
Density Functional Theory Study of the Structure and Energetics of Negatively Charged Oligopyrroles
Department of Computational and Data Sciences, George Mason University, MS 6A2, Fairfax, VA 22030
International Journal of Quantum Chemistry (Impact Factor: 1.17). 08/2011; 111(10):2295  2305. DOI: 10.1002/qua.22659 Fulltext
Estela BlaistenBarojas, May 14, 2014 Available from: Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

 "Results closest to experiment [38] [26] are obtained with B3PW91, reproducing the experimental planar structure of pyrrole (Py) with the smallest error of 1.0%. The B3PW91 approach is then adopted, which additionally allows for comparison with our previous studies [23] [24] [25]. The Py molecule is a C 2v planar structure with a strong dipole moment of 1.94D in the direction of the NAH bond and À23.5, À26.8, À34.4D Å for the diagonal elements of the quadrupole matrix. "
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ABSTRACT: A series of oligopyrrole dications, nPy2+nPy2+, n = 1–12, 15, 18, 21, 24, 27 are studied with hybrid density functional theory at the B3PW91/631+G(d,p) level. Geometry optimization and electronic structure of oligopyrrole dications are revisited using spinrestricted and spinunrestricted methods. It is found that the ground states of short oligopyrrole dications nPy2+nPy2+ (n < 7) are spinrestricted singlet ground states. Thus, the charge carrier in these molecular dications has characteristics of a bipolaron. In contrast, medium size oligopyrrole dications (7⩽n⩽15)(7⩽n⩽15) have a spinunrestricted singlet ground state and display charge carriers that have a polaron pair character. With increasing oligomer length, the spinunrestricted singlet and the triplet become degenerate such that for even longer oligopyrrole dications (nPy2+,n⩾18)(nPy2+,n⩾18) the ground state is a triplet and the charge carrier is predominantly a polaron pair.Computational and Theoretical Chemistry 08/2012; 993:7–12. DOI:10.1016/j.comptc.2012.05.018 · 1.37 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A classical model potential to simulate pyrrole oligomers in condensed phases is developed in this work. The new potential contains ten parameters that are optimized on a database of energy points calculated within the density functional theory approach. Based on this potential the condensed phase of systems composed of pyrrole oligomers with 4 and 12 monomers is studied as a function of system density. The binding energy, endtoend distance, radius of gyration, vector and orientational order parameters, and pair correlation functions are reported at T=300 K. The mechanical equilibrium density is determined for both systems. The bulk modulus is reported at these densities, showing that systems composed of short oligomers are softer than systems containing longer oligomers. Analysis of pair correlation functions and order parameters indicates that at equilibrium the system of short oligomers has characteristics of a liquid while the system of longer oligomers shows a chain stacking trend.The Journal of Chemical Physics 07/2010; 133(3):034905. DOI:10.1063/1.3457675 · 3.12 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Six isomers of dipicolinic acid (DPA) in the gas phase are predicted based on a detailed density functional theory study. Energetics include the binding energy, ionization potential, and electron affinity. Dipole moments, rotational constants, atomic charges, and Fukui functions are also calculated. Several isomerization reactions are shown as possible, with calculated reaction path and transition barriers in the range 6–14kcal/mol. Prediction of five DPA dimers and three crystalline DPA polytypes are also reported. Vibrational analysis for monomers and dimers is calculated and compared to existing experimental results. The electronic band structure of three crystalline polytypes shows that DPA crystals are insulators. The three stable polytypes display distinct hydrogenbonding formations that originate sheets of DPA molecules that are further stacked to form layered crystals that are energetically nearly degenerate.Computational and Theoretical Chemistry 12/2011; 977(s 1–3). DOI:10.1016/j.comptc.2011.09.030 · 1.37 Impact Factor