Ionization Potential, Electron Affinity, Electronegativity, Hardness, and Electron Excitation Energy:  Molecular Properties from Density Functional Theory Orbital Energies

Abstract

Representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, have been studied by using density functional theory. The calculations were done with the commonly used exchange-correlation functional B3LYP followed by a comprehensive analysis of the calculated highest-occupied and lowest-unoccupied Kohn-Sham orbital (HOMO and LUMO) energies. The basis set dependence of the DFT results shows that the economical 6-31+G* basis set is generally sufficient for calculating the HOMO and LUMO energies (if the calculated LUMO energies are negative) for use in correlating with molecular properties. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity ( ), hardness (η), and first electron excitation energy (τ) are all in good agreement with the available experimental data. A generally applicable linear correlation relationship exists between the calculated HOMO energies and the experimental/calculated IPs. We have also found satisfactory linear correlation relationships between the calculated LUMO energies and experimental/calculated EAs (for the bound anionic states), between the calculated average HOMO/LUMO energies and values, between the calculated HOMO-LUMO energy gaps and η values, and between the calculated HOMO-LUMO energy gaps and experimental/ calculated first excitation energies. By using these linear correlation relationships, the calculated HOMO and LUMO energies can be employed to semiquantitatively estimate ionization potential, electron affinity, electronegativity, hardness, and first excitation energy.

Procainamide, but notN-Acetylprocainamide, Induces Protein Free Radical Formation on Myeloperoxidase: A Potential Mechanism of Agranulocytosis

“…We have shown above that NAPA has a greater ionization potential than PA. Ionization potential has been shown to have a linear relationship with energy of the highest occupied molecular orbital (50), and Koopman's theorem states that the latter is equal to the first ionization potential. Ionization potential is also related linearly to the oxidation potential (51).…”

Asymptotic correction of the exchange–correlation kernel of time-dependent density functional theory for long-range charge-transfer excitations

“…8 and 9, and are in fact negative for all of the small molecules considered here, but they tend to decrease for larger basis sets used. 9 Having in mind this tendency and anticipating that in the considered molecules an extra electron should occupy a weakly bound level, we also present in Table I A . According to ͑6͒, this will lead to a large underestimation of the excitation energy a Ϫ d ϭ CT TDDFT(0) with the zero-order TDDFT.…”

Molecular dynamics and density functional theory study on the corrosion inhibition of austenitic stainless steel in hydrochloric acid by two pyrimidine compounds

“…These calculations were performed to investigate the structural parameters that affect the inhibition efficiency of the two pyrimidine derivatives and also to study the adsorption mechanisms on the austenitic stainless steel surface. From the optimized geometries of BCPTI and BTPTT, their global molecular descriptors [31][32][33][34][35][36][37][38][39][40][41][42][43][44] such as the energy of the highest occupied molecular orbital (E HOMO ), the energy of the lowest unoccupied molecular orbital (E LUMO ), the energy gap (DE), the ionization potential (IP), the electron affinity (EA), the global hardness (g), the electronegativity (v), the global softness (r), the electrophilicity (x), the electrodonating (x -), the electroaccepting (x ? ), the net electrophilicity (Dx ± ), the fraction of electron transferred (DN), the total negative charge (TNC) and the dipole moment (l) were calculated.…”