  We consider non-relativistic electron correlation energies of heavy noble gas
atoms including the superheavy element Og. The corresponding data enables us to
quantify fixed-node errors in real space quantum Monte Carlo methods as a
function of the atomic number $Z$. We confirm that single-reference trial
function nodes lead to an overall trend of mild decrease in recovered
correlation energy with the increasing $Z$. This agrees with our previous study
that has shown increasing fixed-node biases with the increasing electron
density. We also estimate the value of the linear term in the asymptotic
expansion of the atomic correlation energy.
