The model effective Hamiltonian for electronic structure of Ni2+ aqueous solution [S. Iuchi, A. Morita, S. Kato, J. Chem. Phys. 121 (2004) 8446] is revised to include the spin-orbit coupling effects. In order to investigate the performance of the revised model Hamiltonian, the electronic absorption spectrum is computed through molecular dynamics simulations. The simulated spectrum is in a reasonable agreement with the experimental one including the band splitting originating from the spin-orbit coupling. This result indicates that the modified Hamiltonian reasonably describes the mixing of different spin states. (C) 2009 Elsevier B. V. All rights reserved.