Density-matrix renormalization-group calculations of excited states of linear polyenes

Journal article

We present density-matrix renormalization-group calculations of the Pariser-Parr-Pople-Peierls model of linear polyenes within the adiabatic approximation. We calculate the vertical and relaxed transition energies, and relaxed geometries for various excitations on long chains. The triplet (1 3Bu+) and even-parity singlet (2 1Ag+) states have a 2-soliton and 4-soliton forms, respectively, both with large relaxation energies. The dipole-allowed (1 1Bu-) state forms an exciton-polaron, and has a very small relaxation energy. The relaxed energy of the 2 1Ag+ state lies below that of the 1 1Bu- state. We observe an attraction between the soliton-antisoliton pairs in the 2 1Ag+ state. The calculated excitation energies agree well with the observed values for polyene oligomers; the agreement with polyacetylene thin films is less good, and we comment on the possible sources of the discrepancies. The photoinduced absorption is interpreted. The spin-spin correlation function shows that the unpaired spins coincide with the geometrical soliton positions. We study the roles of electron-electron interactions and electron-lattice coupling in determining the excitation energies and soliton structures. Electronic interactions play the key role in determining the ground-state dimerization and the excited-state transition energies.

Authors: Barford, W; Bursill, R; Lavrentiev, M

• Publication status: Published
• Journal: Physical Review B
• Volume: 63
• Issue: 19
• Pages: 1951081-1951082
• Publication date: 2001-05-15
• DOI: 10.1103/PhysRevB.63.195108
• EISSN: 1095-3795
• ISSN: 1098-0121
• Language: English