where Mi, RiA, and i are the nucleus mass, expected position value, and Gaussian width. This is an approximation commonly employed in quantum molecular dynamics simulations to describe the nuclear wave function of a molecule. Note that, despite the formal similarity, the Gaussian length i -1/2 should not be mistaken for the correlation length rC discussed in the continuous spontaneous localization model (CSL) literature (see, for instance, refs. ) and experimentally estimated. We show in Appendix B that using and (5) neglecting the electron masses, E becomes