We check the validity of the first principles molecular dynamics simulation using the time-dependent Kohn-Sham equation on the basis of the time-dependent density functional theory coupled with the Newtonian equation of motion, in a special case of a chemical reaction, H-2 + F-2 <-> 2HF, which occurs by the double excitation lifting two electrons from the highest occupied molecular orbital level to the lowest unoccupied molecular orbital level. We find that the method is valid in special case where the reaction proceeds in the relaxation: the electronic excited state changes diabatically into the electronic ground state without non-adiabatic transitions. (c) 2005 Elsevier B.V. All rights reserved.