  In this work, atomic calculations were performed within the local-density and
generalized-gradient approximations of exchange and correlation density
functionals within density-functional theory to provide accurate periodic
trends of first ionization energies and electron affinities of the atomic
series from hydrogen to xenon. Electronegativities were determined directly
from Mulliken's formula and were shown to be equivalently calculated rather by
using Slater-Janak's transition state or by calculating the electrostatic
self-energies of the orbitals involved in the transition to ions. Finally,
comparisons were made with other theoretical and experimental results,
including Mulliken-Jaff\'e's electronegativity scale.
