By using TDDFT and the mixed LE-CTE exciton model with and without the interaction Moreover, we checked the effect of aggregate size on the spectra. The calculations show that the ECD spectra of oligomers are more sensitive to the oligomer size than the absorption spectra, and they exhibit an odd-even alternation pattern as the number of molecular units varies. For the larger aggregates, we construct their electronic Hamiltonians in the diabatic representation by using the information of diabatic states of tetramer. The resulting result for hexamer based on this Hamiltonian is nearly consistent with TD-DFT calculation as the result demonstrated in SI. The deviation is attributed to the approximation introduced in building the Hamiltonian. During the construction, we explicitly considered the boundary effects of the finite-size oligomers and applied the parameters of two units in the middle of tetramer to extend the system's Hamiltonian.