Some Approximate Kohn-Sham Molecular Energy Formulas

Politzer, Peter; Abu-Awwad, Fakher

doi:10.21236/ada343015

Cited by 43 publications

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“…For almost all of the commonly used exchange-correlation functionals, the negative of the HOMO energy is not close to the exact IP, in contrast to the results of Hartree-Fock (HF) theory for which Koopmans' theorem is valid. 17 Although the IP given by the negative of the DFT HOMO energy with typical exchange-correlation functionals is usually too small, it has been shown that the KS orbitals can be related to experimental IPs by a constant shift. 18 Politzer et al showed that the experimental IPs for 9 monosubstituted benzene derivatives linearly correlate with both the HF HOMO energies and the DFT HOMO energies.…”

Section: Introductionmentioning

confidence: 99%

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

2003

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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.

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Section: Introductionmentioning

confidence: 99%

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

2003

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“…Although the question about the physical content of the KS orbital energies raised a scientific debate [6], theoretical justification for this result was given by Baerends and co-workers [7,8] and by Bartlett and co-workers [9,10]. Unfortunately, orbital energies from approximate functionals tend to underestimate substantially the IPs of molecular systems [11,12].…”

Section: Introductionmentioning

confidence: 99%

Local reduced-density-matrix-functional theory: Incorporating static correlation effects in Kohn-Sham equations

et al. 2014

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We propose a scheme to bring reduced-density-matrix-functional theory into the realm of density functional theory (DFT) that preserves the accurate density functional description at equilibrium, while incorporating accurately static and left-right correlation effects in molecules and keeping the good computational performance of DFT-based schemes. The key ingredient is to relax the requirement that the local potential is the functional derivative of the energy with respect to the density. Instead, we propose to restrict the search for the approximate natural orbitals within a domain where these orbitals are eigenfunctions of a single-particle Hamiltonian with a local effective potential. In this way, fractional natural occupation numbers are accommodated into Kohn-Sham equations allowing for the description of molecular dissociation without breaking spin symmetry. Additionally, our scheme provides a natural way to connect an energy eigenvalue spectrum to the approximate natural orbitals and this spectrum is found to represent accurately the ionization potentials of atoms and small molecules.

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“…This finding implies that both the introduction of Benzothiadiazole unit and the elongation of π-conjugation length can enhance the light-harvesting ability of a photosensitizing dye, providing a beneficial concept of material design for fabricating panchromatic DSSCs. (5) The required energy to remove one electron from a neutral material can be specified by IP and the capacity of the material to accept one electron from the environment is EA [54]. In simple molecular orbital theory approaches as proposed by Koopmans theorem, the HOMO and LUMO energy level are related to the IP and EA, respectively [54] (Eq.…”

Section: Uv/vis Absorption Spectramentioning

confidence: 99%

“…(5) The required energy to remove one electron from a neutral material can be specified by IP and the capacity of the material to accept one electron from the environment is EA [54]. In simple molecular orbital theory approaches as proposed by Koopmans theorem, the HOMO and LUMO energy level are related to the IP and EA, respectively [54] (Eq. (6)): and…”

Section: Uv/vis Absorption Spectramentioning

confidence: 99%

Low Band Gap of Novel Compounds Having Triphenylamine and Oligothiophenes Based Donor-acceptor Organic Dyes for Photovoltaic Applications: A DFT-B3LYP Calculation

et al. 2017

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Some Approximate Kohn-Sham Molecular Energy Formulas

Cited by 43 publications

References 0 publications

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

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

Local reduced-density-matrix-functional theory: Incorporating static correlation effects in Kohn-Sham equations

Low Band Gap of Novel Compounds Having Triphenylamine and Oligothiophenes Based Donor-acceptor Organic Dyes for Photovoltaic Applications: A DFT-B3LYP Calculation

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