[¦bȯrn ′äp·ən‚hī·mər ə‚präk·sə‚mā·shən] (physical chemistry) The approximation, used in the Born-Oppenheimer method, that the electronic wave functions and energy levels at any instant depend only on the positions of the nuclei at that instant and not on the motions of the nuclei. Also known as adiabatic approximation.AcronymsSeebest of all