F. Aryasetiawan, O. Gunnarsson, A. Rubio

We study the  ¹S_g⁺ --> ¹S_g⁺ excitation for a H₂ molecule as a function of the nuclear distance d in the time-dependent local-density approximation. We find rather accurate results for intermediate d but not for small and large d.  The spin-dependent formalism gives a qualitative improvement for large d.  The results are analyzed by comparing with the 2s --> 2p excitation for He, Li and Be for small and intermediate d and by comparing with the Hubbard model for large d.  The fairly accurate results for Li and Be are related to the accuracy of the ground-state formalism for a few electrons.