Kinetic contribution to the correlation energy density: benchmark to Tc[n] energy functionals

Properties of atoms in electronically excited molecules within the formalism of TDDFT

The topological analysis of the electron density for electronic excited states under the formalism of the quantum theory of atoms in molecules using time-dependent density functional theory (TDDFT) is presented. Relaxed electron densities for electronic excited states are computed by solving a Z-vector equation which is obtained by means of the Sternheimer interchange method. This is in contrast to previous work in which the electron density for excited states is obtained using DFT instead of TDDFT, that is, through the imposition of molecular occupancies in accordance with the electron configuration of the excited state under consideration. Once the electron density of the excited state is computed, its topological characterization and the properties of the atoms in molecules are obtained in the same manner that for the ground state. The analysis of the low-lying π→π* singlet and triplet vertical excitations of CO and C6H6 are used as representative examples of the application of this methodology. Altogether, it is shown how this procedure provides insights on the changes of the electron density following photoexcitation and it is our hope that it will be useful in the study of different photophysical and photochemical processes.

Atomic Partitioning of the Dissociation Energy of the P−O(H) Bond in Hydrogen Phosphate Anion (HPO42-): Disentangling the Effect of Mg2+

This paper has three goals: (1) to provide a first step in understanding the atomic basis of the role of magnesium in facilitating the dissociation of the P-O bond in phosphorylated biochemical fuel molecules (such as ATP or GTP), (2) to compare second-order Møller-Plesset perturbation theory (MP2) results with those obtained at the more economical density functional theory (DFT) level for a future study of larger more realistic models of ATP/GTP, and (3) to examine the calculation of atomic total energies from atomic kinetic energies within a Kohn-Sham implemention of DFT, as compared to ab initio methods. A newly described method based on the quantum theory of atoms in molecules (QTAIM), which is termed the "atomic partitioning of the bond dissociation energy" (APBDE), is applied to a simple model of phosphorylated biological molecules (HPO42-). The APBDE approach is applied in the presence and in the absence of magnesium. It is found that the P-O(H) bond in the magnesium complex is shorter, exhibits a higher stretching frequency, and has a higher electron density at the bond critical point than in the magnesium-free hydrogen phosphate anion. Though these data would seem to suggest a stronger P-O(H) bond in the magnesium complex compared to the magnesium-free case, the homolytic breaking of the P-O(H) bond in the complex is found to be easier, i.e., has a lower BDE. This effect is the result of the balance of several atomic contributions to the BDE induced by the magnesium cation, which stabilizes the dissociation product more than it stabilizes the intact model molecule.