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A density matrix renormalization group study of low-lying excitations of polythiophene within a Pariser-Parr-Pople model

Das, Mousumi and Ramasesha, S (2006) A density matrix renormalization group study of low-lying excitations of polythiophene within a Pariser-Parr-Pople model. In: International Conference on Recent Developments in Metal Oxides and Related Materials,, Jan 09-11, 2006, Bangalore, India, pp. 67-78.

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Abstract

Symmetrized density-matrix-renormalization-group calculations have been carried out, within Pariser-Parr-Pople Hamiltonian, to explore the nature of the ground and low-lying excited states of long polythiophene oligomers. We have exploited C-2 symmetry and spin parity of the system to obtain excited states of experimental interest, and studied the lowest dipole allowed excited state and lowest dipole forbidden two photon state, for different oligomer sizes. In the long system limit, the dipole allowed excited state always lies below the lowest dipole forbidden two-photon state which implies, by Kasha rule, that polythiophene fluoresces strongly. The lowest triplet state lies below two-photon state as usual in conjugated polymers. We have doped the system with a hole and an electron and obtained the charge excitation gap and the binding energy of the 1(1)B(u)(-) exciton. We have calculated the charge density of the ground, one-photon and two-photon states for the longer system size of 10 thiophene rings to characterize these states. We have studied bond order in these states to get an idea about the equilibrium excited state geometry of the system. We have also studied the charge density distribution of the singly and doubly doped polarons for longer system size, and observe that polythiophenes do not support bipolarons.

Item Type: Conference Paper
Additional Information: Copyright of this article belongs to Indian Academy of Sciences.
Keywords: DMRG technique; PPP Hamiltonian; low-lying excited states; fluorescence; Kasha rule.
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 06 Sep 2010 05:02
Last Modified: 19 Sep 2010 06:15
URI: http://eprints.iisc.ernet.in/id/eprint/31840

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