Integrate Laplacian operator by parts

[Eric_J]

This is the key step to transform from position space Schrödinger equation to its counterpart in momentum space.
How is the first equation transformed into 3.21?
To be more specific, how to integral Laplacian term by parts?

 

[dextercioby]

Do you know tensor tensor calculus or at least the Gauss-Ostrograski theorem in 3D?

 

[Eric_J]

Do you know tensor tensor calculus or at least the Gauss-Ostrograski theorem in 3D?

Thanks for the hint!