Density matrix renormalisation group calculations of molecular exciton energies in poly( p-phenylene vinylene)

• Published in: Synthetic metals 1997-03, Vol.85 (1), p.1155-1156
• Main Authors: Barford, W., Bursill, R.J.
• Format: Article
• Language: English
• Subjects: Applied sciences; Electrical, magnetic and optical properties; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Semi-empirical models and model calculations
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/S0379-6779(97)80192-0

Starting from the Pariser-Parr-Pople model of π-conjugated systems, we construct a model of the low lying excitations of poly( p-phenylene vinylene). The model is based on the bonding HOMO and LUMO states of the molecular repeat units. The model is numerically tractable in that it is solved for oligomers of up to 15 units using the density matrix renormalisation group method. The energy of the 1 1B u − exciton is in good agreement with oligomers, and approaches ca. 2.7 eV. for oligomers of 15 units. Likewise, we predict a 2 1A g + exciton at ca. 2.8 eV, a 1 3B u + exciton at 1.6 eV and the singlet exciton binding energy as being 1.4 eV for single chains. We extend this approach to target other absorption bands. For example, we find a localised Frenkel exciton at 5.8 eV, in excellent agreement with the 6 eV absorption peak in PPV.