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

Abstract

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.

Stilbene photoisomerization driving force as revealed by the topology of the electron density and QTAIM properties

“…measure of the mean electronegativity of the system along the part of the reaction profile between the cis isomer and the conical intersection. In other words, r is the resistance to the transfer of electrons within the atoms in a molecule occurring with the change of electron configuration, and it reflects the process of removal and insertion of electron density in different parts of the molecule, which can be related to ionization potentials and electron affinities [27]. As shown in Fig.…”

Ultrafast excited state hydrogen atom transfer in salicylideneaniline driven by changes in aromaticity

“…5,27 We investigated the reactivity in the ground and the first singlet excited states of SA by means of the Quantum Theory of Atoms in Molecules (QTAIM). 28 The nature of the transferred species in the ESIPT of SA was examined through the Laplacian of the electron density, ∇ 2 ρ(r), in both S 0 and S 1 electronic states. We decided to use quantum chemical topology (QCT) techniques because they have proven to offer valuable insights about photophysical 28 and photochemical 29 processes.…”

“…28 The nature of the transferred species in the ESIPT of SA was examined through the Laplacian of the electron density, ∇ 2 ρ(r), in both S 0 and S 1 electronic states. We decided to use quantum chemical topology (QCT) techniques because they have proven to offer valuable insights about photophysical 28 and photochemical 29 processes. In addition, QCT methods are particularly suitable for this investigation because electronically excited states have bond orders and other descriptors of the electronic structure of a molecule drastically altered in comparison with those in the electronic ground state.…”

“…The exchange-correlation functional τHCTH-hyb 30 along with the 6-311G++(d,p) basis set were considered throughout this work, because their joint utilization has provided a good description of excited electronic states in organic molecules. 28 The choice of this functional was also based on the fact that it describes very well the emission and absorption of SA in cyclohexane, which are the experimental values taken as reference (Table S1 in the Supporting Information). The results obtained with τHCTH-hyb are to be contrasted with those computed with range separated-functionals like CAM-B3LYP 31 and LC-BLYP 32 which have considerably large errors (up to 0.79 and 0.74 eV for the absorption and emission respectively) with respect to the experimental value.…”

“…More precisely, atomic energies were calculated by considering the virial ratio and the Kohn-Sham noninteracting kinetic energy. 28 The examination of the QTAIM properties and ∇ 2 ρ(r) for the ground S 0 and the excited state S 1 was performed using the AIMAll package. 34 We first consider the potential energy curves for the prototropic tautomerism of salicylideneaniline in the S 0 and S 1 states as shown in Figure 1.…”