Note that time evolution of the nuclear coordinate ( ⃗ R(t), ⃗ P (t)) depicts a classical trajectory moving on the active surface V λ in the nuclear phase space. Along the trajectory, the electronic wavefunction can be expressed as |ψ(t)⟩ = J C J (t) Ψ J ( ⃗ R(t)) and the quantum amplitude C J (t) follows the electronic Schrodinger equation