We investigate three generally used exchange-correlation functions (good for most other properties) in order to discern their ability to reproduce ground-state total energies of highly ionized atoms as well as the sum of their first two ionization energies. Total ground-state energies of closed shell atoms with TV electrons and Z atomic numbers are considered for 2≤N≤Z≤18, and N=2,4,6,8,10. The sum of the first two ionization energies, I1+I2, is calculated for closed shell atoms with Z=2,4,6,8,10. The density functional theory (DFT) methods investigated are remarkably successful in accounting for the ground-state total energy of the ionized states of atoms, although their accuracy significantly varies with the positive charge of the ionized atom. Interestingly, the conventional Hartree-Fock self-consistent field (HF-SCF) method is more "rigid" with respect to this type of variance in accuracy. The Becke gradient corrected exchange function gives good results, but the Becke exchange with the Lee-Yang-Parr correlation function is better. However, there are some ionized states of atoms for which even the best density functional methods do not exceed the accuracy of the conventional Hartree-Fock SCF method. The simple Dirac- Slater functional gives poor results. The comparison of these methods to accurate ab initio calculations and experimental data are reported in detail. Interestingly, the accuracy of these methods (as a function of the degree of ionization) may reflect the shell structure of the atom.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry