# Time-dep perturbation theory

1. Nov 16, 2007

### omyojj

while Im reading the griffiths textbook..

got my curiosity from "Typically, the diagonal matrix elements of H vanish"

i.e. <a|H|a>=0 in general..

If V(x) does not have an angular dependence..

the selection rule implies <a|H|a>=0 (since Δl=0)..yes..

but what if it does?

what it(vanishing diagonal element of H) means
physically (in view of the perturbation theory)

sorry for my bad english..

2. Nov 16, 2007

### Dr Transport

If the diagonal elements of the perturbation didn't vanish, then they wouldn't perturb the system but be a small addtion to the unperturbed eigenvalue or another eigenstate.

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