π-Electron Calculations Using the Local Linear-Response Coupled-Cluster Singles and Doubles Theory

Calculations of electronic excitation energies, electron charge distribution, and optical parameters for π-conjugated oligomeric systems are carried out with a new local semiempirical π-electron variant of the coupled clusters (CC) theory involving single and double excitations. The results obtained in the calculations demonstrate adequate accuracy of the proposed linear-response generalization of the local semiempirical π-electron CC approach employing covalently nonbonded molecules of ethylene as the basis set in the calculation. Limit values corresponding to the infinite system size for the lowest excitation energies for polyenes and for condensed and noncondensed polyfulvenes are obtained.