Electronic Structure of Atomic Boron

The electronic structure of the ${}_{}{}^2{}_{}{}^{}P$ ground state of the boron atom has been studied using configuration interaction. A 187-configuration function yielded an energy of -24.6392 hartrees, which corresponds to 88.3% of the correlation energy. The separability of different types of single and double excitations from the Hartree-Fock ground state was investigated. The sum of the energy increments found for single and double excitations amounted to 88.1% of the correlation energy; when the same functions were used simultaneously in a full configuration interaction, the calculated energy included 86.3% of the correlation energy. Triple and quadruple excitations accounted for 2% of the correlation energy. A relatively good five-configuration wave function is also given.