The problem of finding the electron orbits in a molecule is much more complicated than in atoms because the effective potential the electrons feel is no longer approximately spherically symmetric. 1 One can picture the nuclei in a molecule as having classical equilibrium positions – points of minimum potential energy – about which they oscillate slowly, while the electrons travel rapidly around in the Coulomb potential of the nuclei. This simple picture of a molecule works because the nuclei are so much heavier than the electrons; the ratio of the mass m of an electron to the mass M of a nucleus is typically () https://www.w3.org/1998/Math/MathML"> m M ~ 10 − 4   to   10 − 5 . https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429499265/ff9ae276-bf0f-4700-9154-eaa3ea82fbc6/content/eq2609.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>