Evaluation of Absolute Hardness: A New Approach

Abstract

By taking the energy to be a Morse-like function of the number of electrons, E(N) = α{1 - e(-β(N-δ))}(2) - κ, the electronic chemical potential and global hardness values for a set of atoms and some molecules are calculated from the accurate definitions of these two concepts and using the hybrid B3LYP functional and 6-311++G** basis set. By a comparison between the obtained hardnesses and the corresponding experimental values, it is found that the proposed model yields better values for hardnesses with respect to those that are obtained from the other frequently used methods. It is claimed that the difference between the calculated and experimental hardness values may arise from the approximate equation used for the evaluation of experimental hardnesses. Both of the calculated and experimental molecular hardnesses are used to investigate the change of hardness during the course of some exothermic reactions according to the maximum hardness principle (MHP). It is shown that the obtained hardnesses of reactions from the calculated hardnesses (Δη(calc)) are more successful in predicting the directions of these reactions than those that are evaluated from the experimental hardnesses (Δη(exp)).

Assessment of the extended Koopmans' theorem for the chemical reactivity: Accurate computations of chemical potentials, chemical hardnesses, and electrophilicity indices

“…As the second step of our assessment, we consider a set of molecules . For the molecules considered, CPs (in eV) from the HF (KT), EKT‐MP2, EKT‐MP2.5, EKT‐MP3, EKT‐CEPA(0), EKT‐OMP2.5, EKT‐OMP3, and EKT‐OCEPA(0) methods with the aug‐cc‐pVQZ basis set are reported in Table .…”

“…To investigate the performance of the EKT approaches based on post‐HF methods for CHs, we start with the previous set of atoms . For the atoms considered, CHs (in eV) from the HF (KT), EKT‐MP2, EKT‐MP2.5, EKT‐MP3, EKT‐CEPA(0), EKT‐OMP2.5, EKT‐OMP3, and EKT‐OCEPA(0) methods with the aug‐cc‐pVQZ basis set are reported in Table .…”

An explicit approach to conceptual density functional theory descriptors of arbitrary order

“…[31][32][33][34] . The parameters could enter directly into an interpolating function or be weights in an ensemble description, but we will focus mainly on interpolation models in this work.…”

“…, , , (33) and their derivatives with respect to N can be determined by similar techniques to those used for 1 1 12 12 11 , , , , , ,…”

Quantum-chemical model for the formation of the coordination mode structure of Be(II), Ni(II), Pd(II), Pt(II), and Hg(II) bis(chelate) complexes with polydentate azomethine ligands

“…This means that the HSAB principle can be used for the prediction of the comparable stability of compounds (thermodynamic aspect) and the direction of chemical reactions (kinetic aspect). Basically empirical Pearson's concept initiated the development of theoretical models for the descrip tion of the acid-base equilibrium [10][11][12][13][14], including the earliest concept about the controlling effect of frontier molecular orbitals of interacting molecules [11] and the further developed concepts and formulations of the "chemical hardness" of molecules [12][13][14]. At the same time, theoretical substantiations of the main principle of the HSAB concept with respect to the competitive reactivity during the formation of coordi nation metal compounds (i.e., competitive coordina tion) on the basis of data calculated by modern quan tum chemical methods are nearly lacking.…”