Analytical Gradients for Core-Excited States in the Algebraic Diagrammatic Construction (ADC) Framework

Here we present a derivation of the analytical expressions required to determine nuclear gradients for core-excited states at the core-valence separated algebraic diagrammatic construction (CVS-ADC) theory level. Analytical gradients up to and including the extended CVS-ADC(2)-x order have been derived and implemented into a Python module, adc_gradient. The gradients were used to determine core-excited state optimized geometries and relaxed potential energy surfaces for the water, formic acid, and benzne molecules. <br>

Analytical Gradients for Core-Excited States in the Algebraic Diagrammatic Construction (ADC) Framework

Here we present a derivation of the analytical expressions required to determine nuclear gradients for core-excited states at the core-valence separated algebraic diagrammatic construction (CVS-ADC) theory level. Analytical gradients up to and including the extended CVS-ADC(2)-x order have been derived and implemented into a Python module, adc_gradient. The gradients were used to determine core-excited state optimized geometries and relaxed potential energy surfaces for the water, formic acid, and benzne molecules. <br>

Role of Triplet States in the Photodynamics of Aniline

The dynamics of excited heteroaromatic molecules is a key to understanding the photoprotective properties of many biologically relevant chromophores that dissipate their excitation energy nonreactively and thereby prevent the detrimental effects of ultraviolet radiation. Despite their structural variability, most heteroaromatic compounds share a common feature of a repulsive ¹πσ* potential energy surface. This surface can lead to photoproducts, and it can also facilitate the population transfer back to the ground electronic state by means of a ¹πσ*/S₀ conical intersection. Here, we explore a hidden relaxation route involving the triplet electronic state of aniline, which has recently been discovered by means of time-selected photofragment translational spectroscopy [J. Chem. Phys. 2019, 151, 141101]. By using the recently available analytical gradients for multiconfiguration pair-density functional theory, it is now possible to locate the minimum energy crossing points between states of different spin and therefore compute the intersystem crossing rates with a multireference method, rather than with the less reliable single-reference methods. Using such calculations, we demonstrate that the population loss of aniline in the T₁(³ππ^*) state is dominated by C₆H₅NH₂→C₆H₅NH⸱ + H⸱ dissociation, and we explain the long nonradiative lifetimes of the T₁(³ππ^*) state at the excitation wavelengths of 294‑264 nm.

Role of Triplet States in the Photodynamics of Aniline

The dynamics of excited heteroaromatic molecules is a key to understanding the photoprotective properties of many biologically relevant chromophores that dissipate their excitation energy nonreactively and thereby prevent the detrimental effects of ultraviolet radiation. Despite their structural variability, most heteroaromatic compounds share a common feature of a repulsive ¹πσ* potential energy surface. This surface can lead to photoproducts, and it can also facilitate the population transfer back to the ground electronic state by means of a ¹πσ*/S₀ conical intersection. Here, we explore a hidden relaxation route involving the triplet electronic state of aniline, which has recently been discovered by means of time-selected photofragment translational spectroscopy [J. Chem. Phys. 2019, 151, 141101]. By using the recently available analytical gradients for multiconfiguration pair-density functional theory, it is now possible to locate the minimum energy crossing points between states of different spin and therefore compute the intersystem crossing rates with a multireference method, rather than with the less reliable single-reference methods. Using such calculations, we demonstrate that the population loss of aniline in the T₁(³ππ^*) state is dominated by C₆H₅NH₂→C₆H₅NH⸱ + H⸱ dissociation, and we explain the long nonradiative lifetimes of the T₁(³ππ^*) state at the excitation wavelengths of 294‑264 nm.