In this problem, you will use the variational method to find the optimal \(1 s\)
wave function for the hydrogen atom starting from the trial function
\(\Phi(r)=e^{-\alpha r}\) with \(\alpha\) as the variational parameter. You will
minimize
\\[
E(\alpha)=\frac{\int \Phi^{*} \hat{H} \Phi d \tau}{\int \Phi^{*} \Phi d \tau}
\\]
with respect to \(\alpha\)
a. Show that
\\[
\begin{aligned}
\hat{H} \Phi &=-\frac{\hbar^{2}}{2 m_{e}} \frac{1}{r^{2}}
\frac{\partial}{\partial r}\left(r^{2} \frac{\partial \Phi(r)}{\partial
r}\right)-\frac{e^{2}}{4 \pi \varepsilon_{0} r} \Phi(r) \\
&=\frac{\alpha \hbar^{2}}{2 m_{e} r^{2}}\left(2 r-\alpha r^{2}\right)
e^{-\alpha r}-\frac{e^{2}}{4 \pi \varepsilon_{0} r} e^{-\alpha r}
\end{aligned}
\\]
b. Obtain the result \(\int \Phi^{*} \hat{H} \Phi d \tau=4 \pi
\int_{0}^{\infty} r^{2} \Phi^{*} \hat{H} \Phi d r=\)
\(\pi \hbar^{2} /\left(2 m_{e} \alpha\right)-e^{2} /\left(4 \varepsilon_{0}
\alpha^{2}\right)\) using the standard integrals in
the Math Supplement.
c. Show that \(\int \Phi^{*} \Phi d \tau=4 \pi \int_{0}^{\infty} r^{2} \Phi^{*}
\Phi d r=\pi / \alpha^{3}\) using
the standard integrals in the Math Supplement.
d. You now have the result \(E(\alpha)=\hbar^{2} \alpha^{2} /\left(2
m_{e}\right)-e^{2} \alpha /\left(4 \pi \varepsilon_{0}\right)\)
Minimize this function with respect to \(\alpha\) and obtain the optimal value
of \(\alpha\)
e. Is \(E\left(\alpha_{\text {optimal }}\right)\) equal to or greater than the
true
energy? Why?