Mohamed Kahil | Searcharxiv

arXiv2026

A Comparative Study of Correlation and Relativistic Effects on Atomic Ionization Energy

This study investigates the interplay between relativistic effects and electron correlation effects on the first ionization energies of heavy atoms (Au through Rn, Z = 79-86). We perform two complementary analyses: (1) comparing relativistic corrections computed at both the Hartree-Fock (HF) and coupled cluster CCSD(T) levels to assess how correlation influences the magnitude of relativistic corrections, and (2) comparing correlation corrections computed within both non-relativistic and relativistic frameworks to determine how relativity influences the magnitude of correlation corrections. Our results reveal a striking non-linear relationship between these two effects. Specifically, the combined effect of relativity and correlation on ionization energy does not equal the sum of their individual contributions. This non-additivity indicates that relativistic and correlation effects are not independent; they interact in complex ways that depend on the atomic system. We find that for some atoms, the two effects enhance each other, while for others they partially cancel. Moreover, the order in which one may add "separate" effects also counts, in that adding "pure" relativistic effects to the remaining outcome (including correlation) would give a different result than when adding "pure" correlation effects to the remaining outcome (including relativity). These findings demonstrate that relativistic and correlation effects are inherently non-additive, reflecting the non-linearity of the quantum many-body problem. Accurate computational predictions of ionization energies in heavy-element systems thus require simultaneous treatment of both effects rather than treating them as independent contributions.

physics.atom-ph↗

arXiv2025

Relativistic effects on properties of halogen group elements/ions

This srudy investigates the influence of relativistic effects on some properties of the halogen group and gold atoms, including their ions. The analysis covers radii, orbital's energy, first and second ionization energies, electron affinity, and polarizability. The study confirms that the p1/2 orbitals contract under relativistic effects, whereas for the p3/2 orbitals, the mass-velocity and spin-orbit effects do not appear to cancel each other out completely. This may indicate that the spion-orbit effect grows, when increasing the atomic number, slightly faster than the mass-velocity effect. In addition, expansion of the np3/2 orbitals may lead to dilation of the bond length in the related molecules. We found that the non-relativistic Hartree-Fock method gave, for atoms from fluorine to iodine, first ionization energy values with smaller deviations from their experimental ones than other methods involving relativistic and correlation effects. In particular, the method accurately, up to three significative digits, predicts the experimental value for chlorine, and thus can be adopted, discarding other sophisticated methods considering the huge computational effort required by them while not improving much on the agreement with experiment, when evaluating physical-chemical properties of large systems containing light halogen elements. It also predicts an electron affinity of $2.4 eV$ for the tennessine atom, where it shows also that the relativistic effects play a more important role than in gold atoms.

physics.atom-ph↗