Density functional study of double ionization energies.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Atomic and Molecular Physics

Background:

• Accurate calculation of double ionization energies (DIEs) is crucial for understanding atomic and molecular electronic structure.
• Density functional theory (DFT) offers a computationally efficient approach, but the choice of exchange-correlation functional significantly impacts accuracy.

Purpose of the Study:

• To systematically evaluate various exchange-correlation (xc) functionals within DFT for calculating DIEs of gas-phase atoms and molecules.
• To identify the most accurate functionals for DIE calculations, distinguishing between atomic and molecular systems.

Main Methods:

• Calculated DIEs using the energy difference method with DFT.
• Tested 59 exchange-correlation energy functionals (E xc) on 24 main group atoms and 29 molecules.
• Employed an approximation involving statistical average of orbital potentials for electron density calculation.

Main Results:

• For atoms, non-hybrid functionals like Perdew-Burke-Ernzerhof (modified) and Krieger-Chen-Iafrate-Savin (modified) yielded the lowest average absolute deviation (AAD) of 0.25 eV.
• Surprisingly, hybrid functionals performed poorly for atomic DIEs.
• For molecules, hybrid functionals dominated the top performers, with Becke 1997 (modified by Wilson et al.) achieving an AAD of just under 0.5 eV (0.32 eV excluding outliers).

Conclusions:

• The optimal DFT functional for DIE calculations is system-dependent, with non-hybrid functionals excelling for atoms and hybrid functionals for molecules.
• This work provides valuable guidance for selecting appropriate DFT functionals in electronic structure calculations.
• The findings highlight the need for careful functional selection based on the specific application in computational chemistry.