It is important to note that the coupling elements, C ji , are responsible for the nonadiabatic electronic transitions between any two adiabatic states j and i. Integrating Eq. ( ) gives us the wavefunction coefficients, a j (t), at each time-step, allowing us to completely specify the total wavefunction, |Ψ(r, t) (we already know the adiabatic eigenfunctions at each nuclear step by solving the TISE). As a reminder, the set of {|Φ p (r, R(t)) } is known as an adiabatic basis because it explicitly depends on the nuclear positions, R.