The influence of correlation on the interpretation of Hund's multiplicity rule: A quantum Monte Carlo study

A systematic quantum Monte Carlo study of 2 p atoms (C, N, O) and 3 p atoms (Si, P, S) is performed to investigate the influence of correlation on the interpretation of Hund's multiplicity rule, which is an extension of our previous study of the carbon atom [ J. Chem. Phys. 121 , 7144 ( 2004 ) ] to heavier atoms. The accuracy in the present study is significantly improved as compared with the previous study. A detailed analysis of the correlation contribution to individual energy components of the total energy is given beyond the self-consistent Hartree-Fock calculation. The stability of the highest spin-multiplicity state of all the atoms is ascribed to the greater electron-nucleus attraction energy that is gained at the cost of increasing the electron-electron repulsion energy as well as the kinetic energy. The present study demonstrates that correlation does not change the above conclusion due to the Hartree-Fock theory to support Boyd's less screening mechanism.