Density functional perturbation theory chemical potential

This quantity can be viewed as a generalization of Fukui s frontier molecular orbital (MO) concept [25] and plays a key role in linking Frontier MO theory and the HSAB principle. It can be interpreted either as the sensitivity of a system s chemical potential to an external perturbation at a particular point r, or as the change of the electron density p(r) at each point r when the total number of electrons is changed. The former definition has recently been implemented to evaluate this function [26,27] but the derivative of the density with respect to the number of electrons remains by far the most widely used definition. 

We have now seen that the effort of Parr and collaborators [8-12] to put Fukui s frontier-orbital concept of chemical reactivity on sound footing in density-functional theory through the definition of the Fukui function and the local and global softness works only for extended systems. This restriction to extended systems raises a sixth issue. In both the local softness and the Fukui function, Eqs. (54) and (53a), the orbitals at the chemical potential represent both the LUMO and the HOMO in the Fukui sense. However, there is a continuum of unoccupied KS states above the chemical potential accessible even to weak chemical perturbations any linear combination of which could in principle be selected as the LUMO, and similarly for states below fi and the HOMO. This ambiguity in the frontier-orbital concept obviously applies as well to localized systems when there is more than one KS state significantly affected by a chemical perturbation. 

Since it is possible to calculate an accurate electronic density pg by quantum chemical methods, we may use Vg instead in order to obtain information on p uc according to Eq. (15.90). In this case, we have to use perturbation theory because the terms depending on the electronic density can only be obtained with the unperturbed electronic wave function calculated for an external potential of point-like (or spherically symmetric) nuclei. It can then be assumed... 

Bukowski, R., Szalewicz, K., Groenenboom, G., 8c van der Avoird, A. (2006). Interaction potential for water dimer from symmetry-adapted perturbation theory based on density functional description of monomers. Journal of Chemical Physics, 125, 044301. 

Hesselmann, A., 8c Jansen, G. (2003a). The helium dimer potential from a combined density functional theory and symmetry-adapted perturbation theory approach using an exact exchange-correlation potential. Physical Chemistry Chemical Physics, 5, 5010. 

Misquitta, A. J., Podeszwa, R., Jeziorski, B., Szalewicz, K. (2005b). Intermolecular potentials based on symmetry-adapted perturbation theory with dispersion energies from time-dependent density-functional theory. Journal of Chemical Physics, 123, 214103. 

Combined Quantum Mechanics and Molecular Mechanics Approaches to Chemical and Biochemical Reactivity Complete Active Space Self-consistent Field (CASSCF) Second-order Perturbation Theory (CASPT2) Density Functional Applications Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field Density Functional Theory Applications to Transition Metal Problems Quantum Mechanical/Molecular Mechanical (QM/MM) Coupled Potentials Spectroscopy Computational Methods Transition Metals Applications. 

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