Revealing the regularities of electron correlation energies associated with valence electrons in atoms in the first three rows of the periodic table

TL;DR

This study uncovers regular patterns in electron correlation energies among valence electrons in atoms from helium to argon, revealing that certain correlation components are consistent within the same periodic table row and depend solely on electron orbitals.

Contribution

It demonstrates that inter- and intra-orbital pair-correlation energies are identical for atoms in the same row and depend only on electron orbitals, challenging prior assumptions.

Findings

Correlation energies are consistent within the same row of the periodic table.

Inter-orbital correlation energy is the same for electrons with parallel or anti-parallel spins.

Orbital relaxation effects on correlation energy are minimal.

Abstract

Electronic correlation is a complex many-body effect and the correlation energy depends on the specific electronic structure and spatial distribution of electrons in each atom and molecule. Although the total correlation energy in an atom can be decomposed into different components such as inter-orbital and intra-orbital pair-correlation energies (PCE), it is generally believed that the PCEs in different atoms cannot be the same. In this work, we investigate the correlation energies of the atoms in the first three rows of the periodic table (He to Ar). It is found that when the correlation energy is defined as the difference between the exact ground-state energy and the unrestricted Hartree-Fock (UHF) energy, the inter- and intra-orbital PECs associated with the valence electrons of the atoms in the same row of the periodic table have the same values. These PCEs are not entangled and their values depend only on the electron orbitals. For two specific orbitals, the inter-orbital correlation energy is the same between two electrons of parallel spins or anti-parallel spins. We also show that the effects of orbital relaxation on the correlation energy are surprisingly small.