where cgs is the ground-state wave function. For convenience, we shift the zero level of energy by subtracting the constant Vref from H, where Vref is chosen as the best estimate we have of the ground-state energy Egs. Explain why this shift gives ψ = cgs exp[-τ(Egs-Vref)ψgs. (Use of Vref prevents ψ from becoming very small or very large at large τ.)
(b) Show that the time-dependent Schrödinger equation (7.97) for an n-electron molecule is