# Energy from schrödinger equation

1. Sep 23, 2011

### Gavroy

hi

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

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

2. Sep 23, 2011

### The_Duck

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