Semiempirical quantum chemical studies on neutral and positively charged H(CH)(n)H homologues have been performed for systems with n up to 101, where different kinds of nonlinear excitation are found with increasing chain length. The Pariser-Parr-Pople (PPP) model has been employed and solved with the density matrix renormalization group (DMRG) method. The geometrical and electronic distortions induced by defects are obtained and compared with previous theoretical work, indicating that an adequate account of the electron correlation is essential for describing such systems. The structural distortion of a charged soliton (half-width calculated as L = 13) is shown to be more extended than that of a neutral soliton (L = 6); the geometrical distortion is even more extended in a polaron. In bipolarons, our calculations show that the coupling of the soliton-antisoliton pair might be longer ranged than expected. The phase transition from a bipolaron to a separated soliton-antisoliton pair occurs when n is close to 100.