Relativistic effects on properties of halogen group elements/ions

Abstract This study investigates the influence of relativistic effects on some atomic properties of the halogen group and gold atoms, including their ions (±1). The analysis covers radii, orbital’s energy, first and second ionization energies, electron affinity, and polarizability. The study confirms that the p 1/2 orbitals contract under relativistic effects, whereas for the p 3/2 orbitals, the mass-velocity and spin–orbit effects do not appear to cancel each other out completely. This may indicate that the spin–orbit effect grows, when increasing the atomic number, slightly faster than the mass-velocity effect. In addition, expansion of the np 3/2 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.