Comment on "Frequency-dependent polarizabilities, hyperpolarizabilities, and excitation energies from time-dependent density-functional theory based on the quasienergy derivative method" [J. Chem. Phys. 111, 2878 (1999)]

In this comment we point out the similarity between the recent work of Aiga [J. Chem. Phys. 111, 2878 (1999)] and our work [Phys. Lett. A 236, 525 (19 97)], both developing perturbation methods within time-dependent density-fu nctional theory for calculating frequency-dependent response properties of many-electron systems. (C) 2000 American Institute of Physics. [S0021-9606( 00)30115-X].