The variational method applied to helium gives a better result than the first order perturbation expansion.

for n=1, tex2html_wrap129 . Choose to vary Z as a parameter. (denote as tex2html_wrap130 )

tex2html_wrap131 , tex2html_wrap132 , tex2html_wrap133

This means tex2html_wrap134 . Then tex2html_wrap135 gives tex2html_wrap136 . Then tex2html_wrap137 which gives a closer agreement with experimental results.

tex2html_wrap138 tex2html_wrap139

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