Electron-hole interaction in a polyene

The electron-hole interaction in a polyene is studied both for a short chain and at its thermodynamic limit. We find that there is a competition between the intra- and inter-site interactions for the electron-hole interaction. The former serves as a repulsive force between the electron and hole for a finite-long polyene while the latter as an atttractive interaction. The excitonic states should appear in the system with the electron-hole attractive interaction.