A semi-empirical Hamiltonian with the INDO approximation and CIS was parameterized to reproduce EOM-CCSD excitation energies for diatomic silicon Si-2 with different inter-atomic separations. The model Hamiltonian is transferable, producing excitation energies for clusters, Si-n (n = 3, 4, 5) with mean absolute errors (MAEs) of 0.26, 0.18, and 0.09 eV, respectively, from the EOM-CCSD energies. The absorption spectra are also in qualitative agreement with the EOM-CCSD spectra. For clusters Si-19 and Si-40, comparison with TDDFT gave MAEs of 0.32 and 0.12 eV, respectively. Predictions of excitation energies and absorption spectra are also given for Si-n (n = 124, 147, 172, 779) using the model Hamiltonian.