Excited State Dipole Moments in Solution: Comparison between State-Specific and Linear-Response TD-DFT Values.

We compare different response schemes for coupling continuum solvation models to time-dependent density functional theory (TD-DFT) for the determination of solvent effects on the excited state dipole moments of solvated molecules. In particular, linear-response (LR) and state-specific (SS) formalisms are compared. Using 20 low-lying electronic excitations, displaying both localized and charge-transfer character, this study highlights the importance of applying a SS model not only for the calculation of energies, as previously reported ( J. Chem. Theory Comput. , 2015 , 11 , 5782 , DOI: 10.1021/acs.jctc.5b00679 ), but also for the prediction of excited state properties. Generally, when a range-separated exchange-correlation functional is used, both LR and SS schemes provide very similar dipole moments for local transitions, whereas differences of a few Debye units with respect to LR values are observed for CT transitions. The delicate interplay between the response scheme and the exchange-correlation functional is discussed as well, and we show that using an inadequate functional in a SS framework can yield to dramatic overestimations of the dipole moments.

Metrics for Molecular Electronic Excitations: A Comparison between Orbital- and Density-Based Descriptors.

This study proposes a quantitative and qualitative comparison of two popular metrics used for time-dependent density functional simulations of chromophores when describing absorption and emission processes, with high discrimination power between short- and long-range character of involved electronic excitations and functional performances. To this end, a total of 160 absorption and emission electronic excitations of 80 molecular systems belonging to the "Real-Life Molecules" data set, recently introduced in literature, have been considered a relevant data set. The two selected indexes are based on density (the DCT one) and natural transition orbitals (the ΔrNTO one), respectively. For comparison purposes, an extension of the DCT index, in line with what exists for ΔrNTO, enabling to discriminate electronic transitions occurring in symmetric systems is also proposed. The results show that, independently of the exchange and correlation functional used, a good correlation between the natural transition orbital and density based descriptors is found, thus cross validating their use for the quantification of a large variety of transitions in chemically relevant molecular systems.

Excited state gradients for a state-specific continuum solvation approach: The vertical excitation model within a Lagrangian TDDFT formulation.

The accurate modeling of the environment response is a fundamental challenge for accurately describing the photophysics and photochemistry of molecules both in solution and in more complex embeddings. When large rearrangements of the electron density occur after an electronic transition, state-specific formulations, such as the vertical excitation model, are necessary to achieve a proper modeling of the processes. Such a state-specific model is fundamental not only to obtain accurate energies, but also to follow the geometrical relaxation accompanying the evolution of the excited-states. This study presents the analytical expression of the gradients of the vertical excitation model approach by a Lagrangian formulation in the time dependent density functional theory framework. Representative organic chromophores in solution are used to test the reliability of the implementation and provide comparisons with the linear response description.

Structures and properties of electronically excited chromophores in solution from the polarizable continuum model coupled to the time-dependent density functional theory.

This paper provides an overview of recent research activities concerning the quantum-mechanical description of structures and properties of electronically excited chromophores in solution. The focus of the paper is on a specific approach to include solvent effects, namely the polarizable continuum model (PCM). Such a method represents an efficient strategy if coupled to proper quantum-mechanical descriptions such as the time-dependent density functional theory (TDDFT). As a result, the description of molecules in the condensed phase can be extended to excited states still maintaining the computational efficiency and the physical reliability of the ground-state calculations. The most important theoretical and computational aspects of the coupling between PCM and TDDFT are presented and discussed together with an example of application to the study of the low-lying electronic excited states of push-pull chromophores in different solvents.