Simple DFT Scheme for Estimating Negative Electron Affinities

Abstract

2018) 'Simple DFT scheme for estimating negative electron anities.', Journal of chemical theory and computation., 15 (1). pp. 241-248.The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract A simple density functional theory (DFT) scheme is proposed for estimating negative vertical electron affinities of neutral systems, based on a consideration of the integer discontinuity and density scaling homogeneity. The key feature is the derivation of two system-dependent exchange-correlation functionals, one appropriate for the electron deficient side of the integer and one appropriate for the electron abundant side. The electron affinity is evaluated as a linear combination of frontier orbital energies from self-consistent Kohn-Sham calculations on the neutral system using these functionals. For two assessments comprising a total of 43 molecules, the scheme provides electron affinities that are in good agreement with experimental values and which are an improvement over those from the DFT method of Tozer and De Proft [J. Phys. Chem. A 109 8923 (2005)]. The scheme is trivial to implement in any Kohn-Sham program and the computational cost is that of a series of generalised gradient approximation Kohn-Sham calculations. More generally, the study provides a prescription for performing low-cost, self-consistent Kohn-Sham calculations that yield frontier orbital energies that approximately satisfy the appropriate Koopmans conditions, without the need for exact exchange.

Phenanthrene: establishing lower and upper bounds to the binding energy of a very weakly bound anion

“…There is a vast body of theoretical work that has been done to estimate the stability of very weakly bound, or even unbound, negative anions. 2,18,[22][23][24][25]34,35 We have performed quantum chemical calculations of various Ph complexes using DFT along with the D3 dispersion correction as suggested by Grimme et al 36 Our calculations cannot asses electron affinities quantitatively, among other factors due to their high sensitivity to the zero-point energy correction as already discussed elsewhere. 18 However, results obtained using the oB97XD functional seem to be in reasonable agreement with available experiments.…”

Negative Electron Affinities and Derivative Discontinuity Contribution from a Generalized Gradient Approximation Exchange Functional

“…On the other hand, Vibert and Tozer 34 proposed an extension to the method that led to eq 9, incorporating density scaling homogeneities to derive two system-dependent XC functionals, one appropriate for the electron deficient side of the integer and one appropriate for the electron abundant side. The electron affinity in this case is expressed as in eq 9, but with I and ε L 0 replaced by the eigenvalues of the HOMO and the LUMO, respectively, obtained with the XC functional of the electron deficient side, and ε H 0 replaced by the eigenvalue of the HOMO obtained from the XC functional of the electron abundant side.…”

“…Here we readdress a DFT challenge that was recognized some time ago by Geerlings et al It arises when one asks for a reliable evaluation of the chemical reactivity indices that appear in conceptual DFT. − The issue is negative electron affinities. − The context of the problem is two global descriptors, the chemical potential μ and the hardness η. The chemical potential is the negative of the electronegativity χ as defined through the generalization of Iczkowski and Margrave of Mulliken’s electronegativity .…”

Vibrationally Mediated Stabilization of Electrons in Nonpolar Matter

“…[42][43][44][45] DFT-based techniques were suggested as well. 46,47 However, all these would be impractical for large systems studied in the present work. The physical meaning of the negative ∆KS values is questionable, since we lack the basis set for the continuum part of the wavefunction.…”

“…This is justified only for bound anions, i.e., positive VEA values. Resonances (negative AEA values) can be reliably described by scattering calculations or by a number of approaches using conventional quantum chemical codes together with stabilization techniques. − DFT-based techniques were suggested, as well. , However, all of these would be impractical for large systems studied in this work. The physical meaning of the negative ΔKS values is questionable, because we lack the basis set for the continuum part of the wave function.…”