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Lee, Lee, and Parr (LLP) have shown that the kinetic energy can be written in the same form as Becke's exchange energy. This conjecture of LLP has been generalized to another exchange functional, namely, the Perdew-Wang exchange functional. As demonstrated by Lee and Parr, the exchange energy can be written K=πFFsΓ(r,s)drds with Γ(r,s)=||γ(r,s)||2¯/n2(r), where ||γ(r,s)||2¯ is the spherical average of ||γ(r,s)||2. Using the generalization of LLP's conjecture, it is demonstrated that Γ(r,s)= e-s2/β(r)+a[s4/β02(r)]e-s2/β0(r), a=const, β0(r)=5[3π2n(r)]-2/3. At zeroth order, β(r)=β0(r), the function Γ(r,s), gives exactly the modified Gaussian approximation proposed by Lee and Parr

Ground-state properties of a linear hydrogen-bonded FH...NCH complex are studied by means of the ‘‘freeze-and-thaw’’ cycle of Kohn–Sham Equations with constrained electron density (KSCED) [T. A. Wesolowski and J. Weber, Chem. Phys. Lett. 248, 71, (1996)]. For several geometries of the complex, the electron density and the total energy are compared to the ones obtained by means of the standard Kohn–Sham calculations. The comparisons are made to assess the accuracy of several gradient dependent approximate kinetic energy functionals applied in the KSCED equations. It was found that the closest results to the Kohn–Sham ones were obtained with the functional whose analytical form was proposed by Perdew and Wang for exchange energy [J. P. Perdew and Y. Wang in Electronic Structure of Solids ’91, edited by P. Ziesche and H. Eschrig (Academie Verlag, Berlin, 1991), p. 11] and parametrized by Lembarki and Chermette for kinetic energy [A. Lembarki and H. Chermette, Phys. Rev. A 50, 5328 (1994)]. Around the interaction energy minimum as well as for larger intermolecular distances, the ‘‘freeze-and-thaw’’ cycle of KSCED leads to very similar potential energy surface as the standard supermolecule Kohn–Sham calculations.

The 1,3-intramolecular hydrogen transfer in the HSCH(O) <--> (S)CHOH and HSNO <--> SNOH reactions is studied through density functional theory calculations. The reaction force together with structural and electronic properties is monitored along the reaction path to characterize the mechanism of hydrogen transfer. It is found that in both reactions the hydrogen transfer is activated by the structural rearrangement of the backbone atoms that allow the electrostatic interactions to promote the hydrogen transfer in a stepwise mechanism.

The paper collects the answers of the authors to the following questions: Is the lack of precision in the definition of many chemical concepts one of the reasons for the coexistence of many partition schemes? Does the adoption of a given partition scheme imply a set of more precise definitions of the underlying chemical concepts? How can one use the results of a partition scheme to improve the clarity of definitions of concepts? Are partition schemes subject to scientific Darwinism? If so, what is the influence of a community's sociological pressure in the “natural selection” process? To what extent does/can/should investigated systems influence the choice of a particular partition scheme? Do we need more focused chemical validation of Energy Decomposition Analysis (EDA) methodology and descriptors/terms in general? Is there any interest in developing common benchmarks and test sets for cross‐validation of methods? Is it possible to contemplate a unified partition scheme (let us call it the “standard model” of partitioning), that is proper for all applications in chemistry, in the foreseeable future or even in principle? In the end, science is about experiments and the real world. Can one, therefore, use any experiment or experimental data be used to favor one partition scheme over another? © 2019 Wiley Periodicals, Inc.

This study aims to assess present day density functionals in the description of spin crossover iron(II) complexes. Two recently synthesized spin crossover complexes were considered. Theoretical calculations were made using 53 of the most popular exchange-correlation density functionals with triple zeta plus polarization quality basis sets. The present work shows that even though different density functionals can lead to different energy gaps between spin states, most of them are very similar for these two compounds when a comparison between energy gaps is sought. The present work shows that even though different exchange correlations can lead to different energy gaps between spin states, the difference between these gaps calculated at different geometries and that calculated at a given reference geometry is surprisingly independent of the choice of functional. The reasons for the similarities and the differences among exchange and correlation functional combinations are discussed.

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