Lowest-order correction for the bendulum

1. Feb 27, 2009

eman2009

what is the lowest-order correction to the ground state for the pendulum with small angle?

2. Feb 27, 2009

per.sundqvist

$$cos(x)=1-x^2/2!+x^4/4!-...$$
$$\delta E\propto<\Psi_0\mid x^4\mid\Psi_0>$$