Low lying optically excited states of conjugated polymers with DMRG

We present the results Of a density matrix renormalization group (DMRG) stu dy which reveals the nonlinear optical properties of long chain systems wit hin the extended Hubbard model, We use a combination of the infinite and fi nite system DMRG methods to calculate the dipole couplings between eigensta tes, and are thus able to target the "essential" states which dominate the nonlinear optical response of these materials. Specifically we investigate the 1B(u), optical exciton, the mA(g), (a higher energy even-parity exciton ) and the nB(u) which has previously been identified as the threshold of th e electron-hole continuum.