Ab initioprediction of the electronic and optical excitations in polythiophene: Isolated chains versus bulk polymer

Abstract

initio prediction of the electronic and optical excitations in polythiophene : isolated chains versus bulk polymer. Physical Review B, 61(23), 15817-15826. DOI: 10.1103/PhysRevB.61.15817 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. We calculate the electronic and optical excitations of polythiophene using the GW ͑G stands for one-electron Green function, W for the screened Coulomb interaction͒ approximation for the electronic self-energy, and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. Two different situations are studied: excitations on isolated chains and excitations on chains in crystalline polythiophene. The dielectric tensor for the crystalline situation is obtained by modeling the polymer chains as polarizable line objects, with a long-wavelength polarizability tensor obtained from the ab initio polarizability function of the isolated chain. With this model dielectric tensor we construct a screened interaction for the crystalline case, including both intra-and interchain screening. In the crystalline situation both the quasiparticle band gap and the exciton binding energies are drastically reduced in comparison with the isolated chain. However, the optical gap is hardly affected. We expect this result to be relevant for conjugated polymers in general.

Ab initio dynamics study of poly-para-phenylene vinylene

“…32 A similar permittivity anisotropy can be found for crystalline polythiophene ͑PT͒. 33 In both PPV and PT, the permittivity principal component value ␤ zz is much larger than those in the other directions.…”

Electronic and optical excitations in crystalline conjugated polymers

“…15͒ and 0.6 eV, 16 respectively. We have demonstrated that by embedding a polythiophene chain in a medium with the appropriate frequency-dependent dielectric constants, the exciton binding energy is reduced to 0.76 eV, 13,14 while the optical gap remains virtually unaffected. A similar drastic reduction of the exciton binding energy by interchain screening effects was predicted earlier by Moore and Yaron 17 in polyacetylene, within the semiempirical Pariser-Parr-Pople theory.…”

“…Our numerical implementation has been outlined in our earlier publications. 13,14 We use the Car-Parrinello scheme 23 to obtain the DFT-LDA geometries of the single polymer chains and take the experimental crystal structures. 24,25 For PT this leads to an orthorhombic unit cell with aϭ14.80 ͑chain direction͒, bϭ14.75, and c ϭ10.45 a.u.…”

Electronic and optical excitations in crystalline conjugated polymers

“…15͒ and 0.6 eV, 16 respectively. We have demonstrated that by embedding a polythiophene chain in a medium with the appropriate frequency-dependent dielectric constants, the exciton binding energy is reduced to 0.76 eV, 13,14 while the optical gap remains virtually unaffected. A similar drastic reduction of the exciton binding energy by interchain screening effects was predicted earlier by Moore and Yaron 17 in polyacetylene, within the semiempirical Pariser-Parr-Pople theory.…”

“…Recently, Green's function methods for the first-principles description of the electronic ͑one-particle͒ and optical ͑two-particle͒ excitations of extended systems have been developed and applied to several systems. [9][10][11] In the meantime, these methods have been applied to the conjugated polymers polyacetylene, 12 polyphenylenevinylene 12 ͑PPV͒, and polythiophene 13,14 ͑PT͒. For these three polymers calculations for an isolated polymer chain were performed, leading to a good agreement for the excitation energy of the lowest optically active singlet exciton, but a very large binding energy for this exciton.…”