Home › Forums › density functional theory › the Born-Oppenheimer approximation › if Born-Oppenheimer approximation is not valid This topic has 1 reply, 1 voice, and was last updated 2 years, 2 months ago by biao. Viewing 2 posts - 1 through 2 (of 2 total) Author Posts October 11, 2022 at 6:10 pm #7127 biaoParticipant we will overestimate the H October 11, 2022 at 6:14 pm #7128 biaoParticipant The Born-Oppenheimer approximation is only valid if the electron state is sufficiently separated from the other electron states. The Born-Oppenheimer approximation fails when the electronic states cross or approach. Author Posts Viewing 2 posts - 1 through 2 (of 2 total) You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In