Energy from schrödinger equation

[Gavroy]

hi

i was currently thinking about this step here:

$\langle \psi_n, - \Delta \psi_n \rangle = \int |\nabla \psi_n|^2 dx$

how do you get from the laplacian to this other expression?

 

[The_Duck]

Integrate by parts to move a del operator from the right psi to the left one.