To simplify our notation, we omit R-dependence of the adiabatic electronic states. Plugging the above expansion to time-independent Schödinger equation (TISE) we can obtain the eigenvalue equation for the nuclear wavefunction. The main obstacle is how to write the nuclear kinetic energy operator correctly in the dressed states. We discard the nuclear index α since in our model we only have one nucleus, i.e. ∇ α = ∇. The nuclear gradient operator is applied to the total wavefunction (Eq. 58),