Correlation Energy of theP3Ground State of Neutral Carbon

Many-body perturbation theory is used to calculate a value of -0.156 ± 0.005 a.u. for the correlation energy of the ${}_{}{}^3{}_{}{}^{}P$ ground state of the carbon atom. This value was obtained with a basis set of bound and continuum orbitals of angular momentum $s$, $p$, $d$, and $f$, and the contribution from excitations into states of higher angular momentum is estimated to be less than 2% of this result. A detailed study of three-body correlations is presented; their contribution to the correlation energy is 0.0041 a.u. Special attention is also given to diagrams which produce coupling between the correlation energies of different electron pairs.