Theoretical ab initio investigation of the dipole polarizabilities of oligothiophenes and polythiophene

Abstract

Ab initio coupled and uncoupled Hartree–Fock polarizabilities are computed for increasingly large oligothiophenes using the 3–21G, 6–31G**, 6–311G**, and the Sadlej medium-size polarized atomic basis sets. The comparison with experimental values highlights the large sensitivity of the measured polarizabilities with respect to working conditions. By extrapolating to the infinite chain limit the polarizability values of increasingly large oligomers, we compute the asymptotic polarizabilities per thiophene ring. The transversal, perpendicular, and longitudinal asymptotic coupled Hartree–Fock polarizabilities per thiophene ring are, using the 3–21G (6–31G**) atomic basis set, 49.7 (52.5), 15.2 (20.6), and 184.1 (190.0) a.u., respectively. Polythiophene is more polarizable than polydiacetylene, polyyne, and polysilane but less polarizable than polyacetylene which, in contrast to polythiophene, is much more difficult to process. Using a procedure which relates the polarizability and the topology of the one-particle states, the major contribution to the polarizability is attributed to π-symmetry crystalline orbitals located at the top of the valence bands, which look like an alternation of segments of the highest occupied crystalline orbitals of the all-trans and trans-cisoïd polyacetylene. However, a sizeable σ contribution comes from σ-conjugated segments formed by the sulfur atoms and their two adjacent carbon atoms.

Using magnetic birefringence to determine the molecular arrangement of supramolecular nanostructures

“…This corresponds to the limiting situation of a completely deformed sphere. In this case, we find the maximum calculated birefringence of 3 × 10 −5 at 20 T, which is close to the experimental value of 3.7 × 10 −5 , when using diamagnetic susceptibilities from the addition scheme [21] and the polarizabilities given by Champagne et al [22]. Given the uncertainties in these values, the agreement between the theoretical and experimental values is actually very good.…”

Density functional theory investigation on the electronic structure of furo[3,4-b]pyridine-type heterocyclics: from monomer to polymer

“…Therefore, the geometry and electronic structures of the studied monomers and oligomers are optimized by means of the hybrid DFT method at B3LYP level of theory (Becke-style three-parameter density functional theory) [6,7] with 6-31G(d) [8] basis set in the present article. With homologous polymers, the geometry and electronic properties are calculated by means of the DFT methods for one-dimensional periodic systems [9][10][11][12][13][14][15][16][17]. This was achieved by incorporating in the molecular formalisms the periodic boundary conditions (PBCs) which are a set of boundary conditions that are often used to simulate a large system by modeling a small part that is far from its edge in mathematical models and computer simulations, and distance-based truncation of lattice sums of molecular integrals in a controlled manner (see Trickey et al [18] and Jacquemin et al [19,20] for integral evaluations tailored to lattice sums, Delhalle, Harris, and coworkers [21][22][23][24][25][26] for a Fourier method for lattice sums, Kudin, Scuseria, Champagne and Hirata et al [27][28][29][30][31] for fast multipole methods).…”

Aplicaciones de los métodos computacionales al estudio de la estructura y propiedades de polímeros

“…Cálculos ab initio HF indicaron que ∆<α> es 58.7, 69.5 y 77.0 u.a. cuando el oligómero contiene 2, 3 y 4 anillos de tiofeno, respectivamente [50] . Por otro lado, los resultados obtenidos para oligómeros mayores indicaron que este crecimiento se satura para 7 anillos de tiofeno y ∆<α> converge asintóticamente a 85.1±1.9 u.a.…”