Calculation of ionization potential and chemical hardness: A comparative study of different methods

• Published in: International journal of quantum chemistry Vol. 109; no. 4; pp. 764 - 771
• Main Authors: Shankar, R., Senthilkumar, K., Kolandaivel, P.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 15.03.2009
• Subjects: chemical hardness; electronegativity; ionization potential; Koopman's theorem; statistical average of orbital potential
• ISSN: 0020-7608; 1097-461X
• DOI: 10.1002/qua.21883

The suitability of ab initio and density functional theory (DFT) methods for an accurate determination of ionization potential and chemical hardness is the subject of systematic analysis for a panel of molecules. Comparison of experimental ionization potential values with theoretical results indicates that using orbital energies obtained from the so‐called statistical average of orbital potential (SAOP) model exchange correlation potential in Koopman's theorem is an efficient method to evaluate the correct ionization potentials. Experimental ionization potential and electron affinity values have been used to calculate the absolute chemical hardness. Comparative results show that the chemical hardness values calculated by using Hartree–Fock orbital energies in Koopman's theorem are sufficiently good rather than Möller–Plesset second order perturbation method and DFT‐generalized gradient approximation (GGA) exchange correlation functional orbital energies. A new method given by Tozer et al. (J Phys Chem A 2005, 109, 8923) to calculate the chemical hardness works well with the orbital energies of DFT‐GGA functionals together with the ionization potential values calculated from SAOP orbital energies. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009