J Chem Theory Comput
April 2024
The photochemistry of nitrophenols is a source of smog as nitrous acid is formed from their photolysis. Nevertheless, computational studies of the photochemistry of these widespread toxic molecules are scarce. In this work, the initial photodeactivation of -nitrophenol and -nitrophenol is modeled, both in gas phase and in aqueous solution to simulate atmospheric and aerosol environments.
View Article and Find Full Text PDFJ Chem Theory Comput
January 2024
A methodology to locally characterize conical intersections (CIs) between two adiabatic electronic states for which no nonadiabatic coupling (NAC) vectors are available is presented. Based on the Hessian and gradient at the CI, the branching space coordinates are identified. The potential energy surface around the CI in the branching space is expressed in the diabatic representation, from which the NAC vectors can be calculated in a wave-function-free, energy-based approach.
View Article and Find Full Text PDFJ Chem Theory Comput
July 2022
A procedure for the calculation of spin-orbit coupling (SOC) at the delta self-consistent field (ΔSCF) level of theory is presented. Singlet and triplet excited electronic states obtained with the ΔSCF method are expanded into a linear combination of singly excited Slater determinants composed of ground electronic state Kohn-Sham orbitals. This alleviates the nonorthogonality between excited and ground electronic states and introduces a framework, similar to the auxiliary wave function at the time-dependent density functional theory (TD-DFT) level, for the calculation of observables.
View Article and Find Full Text PDFComputational studies of ultrafast photoinduced processes give valuable insights into the photochemical mechanisms of a broad range of compounds. In order to accurately reproduce, interpret, and predict experimental results, which are typically obtained in a condensed phase, it is indispensable to include the condensed phase environment in the computational model. However, most studies are still performed in vacuum due to the high computational cost of state-of-the-art non-adiabatic molecular dynamics (NAMD) simulations.
View Article and Find Full Text PDFThe decay of cyclopropanone is a typical example of a photodecomposition process. Ethylene and carbon monoxide are formed following the excitation to the first singlet excited state through a symmetrical or asymmetrical pathway. The results obtained with non-adiabatic molecular dynamics (NAMD) using the delta self-consistent field (ΔSCF) method correspond well to previous experimental and multireference theoretical studies carried out in the gas phase.
View Article and Find Full Text PDFAn approach combining subsystem density embedding with the variational delta self-consistent field is presented, which extends current capabilities for excited-electronic-state calculations. It was applied on full-atomic nonadiabatic dynamics of a solvated diimide system, demonstrating that comparable accuracy can be achieved for this system for the investigated configuration space and with a shorter simulation time than the computationally more expensive conventional Kohn-Sham density functional theory-based method. This opens a new pragmatic technique for efficient simulation of nonadiabatic processes in the condensed phase, in particular, for liquids.
View Article and Find Full Text PDFWe present an efficient approach for surface hopping-based nonadiabatic dynamics in the condensed phase. For the systems studied, a restricted Kohn-Sham orbital formulation of the delta self-consistent field (ΔSCF) method was used for efficient calculation of excited electronic states. Time-dependent density functional theory (DFT) is applied to aid excited-state SCF convergence and provide guess electronic state densities.
View Article and Find Full Text PDFThe present work is directed toward understanding the mechanisms of excited state deactivation in three neutral model peptides containing the phenylalanine residue. The excited state dynamics of theγL(g+)folded form of N-acetylphenylalaninylamide (NAPA B) and its amide-N-methylated derivative (NAPMA B) is reviewed and compared to the dynamics of the monohydrated structure of NAPA (NAPAH). The goal is to unravel how the environment, and in particular solvation, impacts the photodynamics of peptides.
View Article and Find Full Text PDFThe excitation wavelength dependent photodynamics of pyrrole are investigated by nonadiabatic trajectory-surface-hopping dynamics simulations based on time dependent density functional theory (TDDFT) and the algebraic diagrammatic construction method to the second order (ADC(2)). The ADC(2) results confirm that the N-H bond dissociation occurring upon excitation at the origin of the first excited state, S1(πσ*), is driven by tunnelling [Roberts et al., Faraday Discuss.
View Article and Find Full Text PDFJ Chem Theory Comput
August 2014
Calculations of CD spectra can provide important structural information for peptide systems. Although TD-DFT is an attractive method for these calculations, recent studies have pointed to problems with modeling charge transfer excitations. Motivated by these problems, we benchmarked the performances of CAM-B3LYP, ωB97X-D, M06-2X, B3LYP, and PBE0 against high level ab initio RICC2 calculations for selected peptide structures.
View Article and Find Full Text PDFKynurenines are UV filters found in the human ocular lens which protect the retina from radiation damage. We report on ab initio investigations of the photochemistry of the cis and trans conformers of kynurenine and of an intramolecularly hydrogen-bonded conformer of 3-hydroxykynurenine O-β-D-glucoside. We have explored the excited-state reaction paths for several radiationless excited-state deactivation processes in kynurenines.
View Article and Find Full Text PDFA conformation-selective photophysics study in phenylalanine model peptides, combining pump-probe gas phase experiments and excited state calculations, highlights for the first time the quenching properties of a primary amide group (through its nπ* excited state) along with the effect of vibrational energy that facilitates access to the conical intersection area.
View Article and Find Full Text PDFThe mechanisms of nonradiative deactivation of a phenylalanine residue after near-UV photoexcitation have been investigated in an isolated peptide chain model (N-acetylphenylalaninylamide, NAPA) both experimentally and theoretically. Lifetime measurements at the origin of the first ππ* state of jet-cooled NAPA molecules have shown that (i) among the three most stable conformers of the molecule, the folded conformer NAPA B is ∼50-times shorter lived than the extended major conformer NAPA A and (ii) this lifetime is virtually insensitive to deuteration at the NH(2) and NH sites. Concurrent time-dependent density functional theory (TDDFT) based nonadiabatic dynamics simulations in the full dimensionality, carried out for the NAPA B conformer, provided direct insights on novel classes of ultrafast deactivation mechanisms, proceeding through several conical intersections and leading in fine to the ground state.
View Article and Find Full Text PDFNonadiabatic dynamics in the framework of time-dependent density functional theory was used to simulate gas-phase relaxation dynamics of pairs of conformations of formic acid monomers (cis and trans FAM) and dimers (acyclic aFAD and cyclic cFAD). In the early phase of the excited state dynamics, elongation of the C═O bond and pyramidalization of the carbon atom is observed in both FAM and FAD. Subsequently, the photodynamics of FAM is shown to be dominated by fragmentation processes occurring mostly in the excited state and resulting in HCO and OH radicals.
View Article and Find Full Text PDFIrradiation of 2-phenyl-1-naphthol (6) in CH(3) CN/D(2) O (3:1) leads to very efficient incorporation of deuterium at the ortho-positions of the adjacent phenyl ring (overall Φ=0.73±0.07), along with minor incorporation at the naphthalene positions 5 and 8.
View Article and Find Full Text PDFThe Schiff base derived from salicylaldehyde and 2-amino-3-hydroxypyridine affords a diversity of solid forms, two polymorphic pairs of the enol-imino (D1 a and D1 b) and keto-amino (D2 a and D2 b) desmotropes. The isolated phases, identified by IR spectroscopy, X-ray crystallography, and (13)C cross-polarization/magnetic angle spinning (CP/MAS) NMR spectroscopy, display essentially planar molecular conformations characterized by strong intramolecular hydrogen bonds of the O-H⋅⋅⋅N (D1) or N-H⋅⋅⋅O (D2) type. A change in the position of the proton within this O⋅⋅⋅H⋅⋅⋅N system is accompanied by substantially different molecular conformations and, subsequently, by divergent supramolecular architectures.
View Article and Find Full Text PDFExtensive computational investigations along with additional quasielastic neutron scattering data were used to obtain a consistent picture of the extensive fluxionality of hydride and dihydrogen ligands in Fe(H)(2)(H(2))(PEtPh(2))(3) over a wide range of temperatures from 1.5 to 320 K. We were able to identify three different regimes in the dynamical processes based on activation energies obtained from line spectral broadening.
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