In quantum chemistry and molecular physics, the Born–Oppenheimer approximation is the assumption that the motion of atomic nuclei and electrons in a molecule can be separated. This approach is based on the fact that the electron mass is much smaller than the mass of the nucleus of its atom, so that their movement around practically does not affect the latter. Thus, the wave function of a molecule can be broken into an electronic component and other nuclear. Calculations can be simplified even more if we consider the stationary atomic nucleus (since it moves much less than the electrons around them).