Charge and bonding redistribution in octatetraene driven by a strong laser field: Time-dependent Hartree–Fock simulation

The time evolution of the reduced single electron density matrix for the π electrons in conjugated molecules in an intense laser field is calculated by numerically integrating the time-dependent Hartree–Fock equations for the Pariser–Parr–Pople model Hamiltonian. We study the field frequency and intensity dependence of the π-electron response, the charge fluctuations with respect to the ground state, and the molecular polarization in unsubstituted and acceptor–donor substituted octatetraene, where we also examine the interaction between a permanent electric dipole moment and the laser field. Our results demonstrate the origin of large nonperturbative changes in the π-electronic charges and bond orders (diagonal and off-diagonal density matrix elements, respectively) induced by a strong laser field.