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Recently, surface‐hopping ab initio molecular dynamics (SH‐AIMD) simulations have come to be used to discuss the mechanisms and dynamics of excited‐state chemical reactions, including internal conversion and intersystem crossing. In dynamics simulations involving intersystem crossing, there are two potential energy surfaces (PESs) governing the motion of nuclei: PES in a spin‐pure state and PES in a spin‐mixed state. The former gives wrong results for molecular systems with large spin‐orbit coupling (SOC), while the latter requires a potential gradient that includes a change in SOC at each point, making the computational cost very high. In this study, we systematically investigate the extent to which the magnitude of SOC affects the results of the spin‐pure state‐based dynamics simulations for the hydride MH2 (M = Si, Ge, Sn, Pb) by performing SH‐AIMD simulations based on spin‐pure and spin‐mixed states. It is clearly shown that spin‐mixed state PESs are indispensable for the dynamics simulation of intersystem crossing in systems containing elements Sn and Pb from the fifth period onward. Furthermore, in addition to the widely used Tully's fewest switches (TFS) algorithm, the Zhu‐Nakamura (ZN) global switching algorithm, which is computationally less expensive, is applied to SH for comparison. The results from TFS‐ and ZN‐SH‐AIMD methods are in qualitative agreement, suggesting that the less expensive ZN‐SH‐AIMD can be successfully utilized to investigate the dynamics of photochemical reactions based on quantum chemical calculations. [ABSTRACT FROM AUTHOR]

In this study, we investigate the autodetachment dynamics of the 1-nitropropane anion after vibrational excitation of the energetically lowest C–H stretching mode using our recently developed extended quantum classical surface hopping approach including the detachment continuum. Therein the detachment from an electronic bound anion state is treated as a nonadiabatic transition into discretized detachment continuum states for an ensemble of classical nuclear trajectories propagated on quantum mechanical potential energy surfaces. The initial ensemble is obtained by sampling a phase space distribution accounting for the vibrational excitation of the C–H stretching mode of the molecule to match the experimental conditions. The simulated kinetic energy distribution of the ejected electrons reproduces characteristic features of the available experimental data. Analysis of the nuclear dynamics points out that the approach to neutral-like geometries with decreased pyramidalization angle of the NO 2 group and reduced the N–O bond lengths are the crucial factors enhancing the ultrafast autodetachment process in vibrationally excited 1-nitropropane. This is facilitated when the dipole-bound first excited state of the anion is populated, which is structurally similar to the neutral system. Although only a small transient population of this state is observed, it acts as an efficient doorway to the detachment continuum and is responsible for a significant amount of the ejected electrons. [ABSTRACT FROM AUTHOR]

As a widely-used sunscreen compound, the caffeic acid (CA) shows the strong UV absorption, while the photoinduced reaction mechanisms behind its photoprotection ability are not fully understood. We try to investigate the photoinduced internal conversion dynamics of CA in order to explore the photoprotection mechanism. The most stable CA isomer is selected to examine its nonadiabatic dynamics using the on-the-fly surface hopping simulations at the semi-empirical level of electronic-structure theory. The dynamics starting from different electronic states are simulated to explore the dependence of the photoinduced reaction channels on the excitation wavelengths. Several S1/S0 conical intersections, driven by the H-atom detachments and the ring deformations, have been found to be responsible for the nonadiabatic decay of the CA. The simulation results show that the branching ratios towards these intersections are modified by the light with different excitation energies. This provides the valuable information for the understanding of the photoprotection mechanism of the CA compound. [ABSTRACT FROM AUTHOR]

Diamondoids, of which adamantane (C 10 H 16 ) is the simplest representative, constitute an intriguing class of carbon based nanomaterials with interesting chemical, mechanical and opto-electronic properties. While neutral diamondoids have been extensively studied for decades, their cationic counterparts were a subject of recent experimental investigations motivated by their potential role in astrochemistry. Here, we perform a computational study of the adamantane cation (C 10 H 16 + ) complementing the recent experimental findings. Specifically, we extend earlier theoretical work on vibrationally resolved electronic spectroscopy by accounting for the higher lying electronically excited states of the cation in the absorption and photoelectron spectra. We also perform adiabatic and nonadiabatic (surface hopping) molecular dynamics simulations to study (fast) fragmentation processes and electronic relaxation of C 10 H 16 + . Our simulations reveal that after excitation with near-infrared–ultraviolet photons, the adamantane cation undergoes an ultrafast internal conversion to the ground (doublet) state (on a time scale of 10–100 fs depending on initial excitation energy) which can be followed by a fast fragmentation, predominantly H loss. The yield of the ultrafast hydrogen dissociation as a function of excitation energy is reported. [ABSTRACT FROM AUTHOR]

The introduction of strong-field ligands can enable luminescence in first-row transition-metal complexes. In this way, earth-abundant near-infrared emitters can be obtained using early 3d metals. A prime example is the molecular ruby [Cr(ddpd)2]3+ (ddpd = N,N′-dimethyl-N,N′-dipyridin-2-ylpyridine-2,6-diamine) that can achieve high phosphorescence quantum yields at room temperature in aqueous solution. To understand these remarkable properties, here, we simulate its photodynamics in water using trajectory surface hopping on linear vibronic coupling potentials parametrized from multiconfigurational CASSCF/CASPT2 calculations. We find that after excitation to the second absorption band, a relaxation cascade through metal-centered states occurs. After an initial back-and-forth intersystem crossing with higher-lying doublet states, the complex relaxes through a manifold of quartet metal-centered states to the low-lying doublet metal-centered states which are responsible for the experimentally observed emission. These electronic processes are driven by an elongation of the Cr–ligand bond lengths as well as the twisting motion of the trans-coordinated pyridine units in the ddpd ligands. The low-lying doublet states are reached within 1–2 ps and are close in geometry to the doublet minima, thus explaining the high phosphorescence quantum yield of the molecular ruby [Cr(ddpd)2]3+. [ABSTRACT FROM AUTHOR]

Cations of diamondoids and derivatives thereof have recently become the subject of experimental, spectroscopic studies due to their potential role in astrochemistry. In particular, their electronic spectra and photoinduced dynamics trigger great interest. Here, we report on computational investigations of two nitrogen-containing derivatives of the adamantane cation (Ada+, C10H16+), the amantadine cation (Ama+, C10H15NH2+) and the 1-cyanoadamantane cation (Ada-CN+, C10H15CN+). Specifically, we study electronic (vibrationally resolved) spectra and nonadiabatic molecular dynamics (modeled using the surface hopping approach based on semiempirical electronic structure theory) of these radical cations. The internal conversion time constants as well as reactive relaxation outcomes (cage-opening and hydrogen loss) are compared for the two derivatives and also with the case of Ada+ [Roy et al., Theor. Chem. Acc.2023, 142, 71]. Remarkably, we find a longer ground-state recovery time for Ada-CN+ than for Ama+ (for the same excitation energy window), despite a smaller excitation energy for the former. Thus, a static energy gap law cannot be used to rationalize nonadiabatic dynamics and excited-state lifetimes in this case: Dynamics and details of the couplings between several states play a decisive role., (© 2024 Wiley‐VCH GmbH.)

The branching corrected surface hopping (BCSH) has been demonstrated as a robust approach to improve the performance of the traditional fewest switches surface hopping (FSSH) for nonadiabatic dynamics simulations of standard scattering problems [J. Chem. Phys. 150, 164101 (2019)]. Here, we study how reliable populations of both adiabatic and diabatic states can be interpreted from BCSH trajectories. Using exact quantum solutions and FSSH results as references, we investigate a series of one-dimensional two-level scattering models and illustrate that excellent time-dependent populations can be obtained by BCSH. Especially, we show that different trajectory analysis strategies produce noticeable differences in different representations. Namely, the method based on active states performs better to get populations of adiabatic states, while the method based on wavefunctions produces more reliable results for populations of diabatic states. [ABSTRACT FROM AUTHOR]

The Born–Oppenheimer approximation, which assumes that the electrons respond instantaneously to the motion of the nuclei, breaks down for a wide range of chemical and biological processes. The rate constants of such nonadiabatic processes can be calculated using analytical theories, and the real-time nonequilibrium dynamics can be described using numerical atomistic simulations. The selection of an approach depends on the desired balance between accuracy and efficiency. The computational expense of generating potential energy surfaces on-the-fly often favours the use of approximate, robust and efficient methods such as trajectory surface hopping for large, complex systems. The development of formally exact non-Born–Oppenheimer methods and the exploration of well-defined approximations to such methods are critical for providing benchmarks and preparing for the next generation of faster computers. Thus, the parallel development of rigorous but computationally expensive methods and more approximate but computationally efficient methods is optimal. This Perspective briefly summarizes the available theoretical and computational non-Born–Oppenheimer methods and presents examples illustrating how analytical theories and nonadiabatic dynamics simulations can elucidate the fundamental principles of chemical and biological processes. These examples also highlight how theoretical calculations are able to guide the interpretation of experimental data and provide experimentally testable predictions for nonadiabatic processes. This article is part of the theme issue 'Chemistry without the Born–Oppenheimer approximation'. [ABSTRACT FROM AUTHOR]

Three methods for non-adiabatic dynamics are compared to highlight their capabilities. Multi-configurational time-dependent Hartree is a full grid-based solution to the time-dependent Schrödinger equation, variational multi-configurational Gaussian (vMCG) uses a less flexible but unrestricted Gaussian wavepacket basis, and trajectory surface hopping (TSH) replaces the nuclear wavepacket with a swarm of classical trajectories. Calculations with all methods using a model Hamiltonian were performed. The vMCG and TSH were also then run in a direct dynamics mode, with the potential energy surfaces calculated on-the-fly using quantum chemistry calculations. All dynamics calculations used the Quantics package, with the TSH calculations using a new interface to a surface hopping code. A novel approach to calculate adiabatic populations from grid-based quantum dynamics using a time-dependent discrete variable representation is presented, allowing a proper comparison of methods. This article is part of the theme issue 'Chemistry without the Born–Oppenheimer approximation'. [ABSTRACT FROM AUTHOR]

The impact of different initial conditions in non-adiabatic trajectory surface hopping dynamics within a hybrid quantum mechanical/molecular mechanics scheme is investigated. The influence of a quantum sampling, based on a Wigner distribution, a fully thermal sampling, based on classical molecular dynamics, and a quantum sampled system, but thermally equilibrated with the environment, is investigated on the relaxation dynamics of solvated fulvene after light irradiation. We find that the decay from the first singlet excited state to the ground state shows high dependency on the initial condition and simulation parameters. The three sampling methods lead to different distributions of initial geometries and momenta, which then affect the fate of the excited state dynamics. We evaluated both the effect of sampling geometries and momenta, analysing how the ultrafast decay of fulvene changes accordingly. The results are expected to be of interest to decide how to initialize non-adiabatic dynamics in the presence of the environment. This article is part of the theme issue 'Chemistry without the Born–Oppenheimer approximation'. [ABSTRACT FROM AUTHOR]

The introduction of strong-field ligands can enable luminescence in first-row transition-metal complexes. In this way, earth-abundant near-infrared emitters can be obtained using early 3d metals. A prime example is the molecular ruby [Cr(ddpd)2]3+ (ddpd = N,N′-dimethyl-N,N′-dipyridin-2-ylpyridine-2,6-diamine) that can achieve high phosphorescence quantum yields at room temperature in aqueous solution. To understand these remarkable properties, here, we simulate its photodynamics in water using trajectory surface hopping on linear vibronic coupling potentials parametrized from multiconfigurational CASSCF/CASPT2 calculations. We find that after excitation to the second absorption band, a relaxation cascade through metal-centered states occurs. After an initial back-and-forth intersystem crossing with higher-lying doublet states, the complex relaxes through a manifold of quartet metal-centered states to the low-lying doublet metal-centered states which are responsible for the experimentally observed emission. These electronic processes are driven by an elongation of the Cr–ligand bond lengths as well as the twisting motion of the trans-coordinated pyridine units in the ddpd ligands. The low-lying doublet states are reached within 1–2 ps and are close in geometry to the doublet minima, thus explaining the high phosphorescence quantum yield of the molecular ruby [Cr(ddpd)2]3+.

Photoinduced carrier dynamic processes are without doubt the main driving force responsible for the efficient performance of semiconductor nano-materials in applications like photoconversion and photonics. Nevertheless, establishing theoretical insights into these processes is computationally challenging owing to the multiple factors involved in the processes, namely reaction rate, material surface area, material composition etc. Modelling of photoinduced carrier dynamic processes can be performed via nonadiabatic molecular dynamics (NA-MD) methods, which are methods specifically designed to solve the time-dependent Schrodinger equation with the inclusion of nonadiabatic couplings. Among NA-MD methods, surface hopping methods have been proven to be a mighty tool to mimic the competitive nonadiabatic processes in semiconductor nanomaterials, a worth noticing feature is its exceptional balance between accuracy and computational cost. Consequently, surface hopping is the method of choice for modelling ultrafast dynamics and more complex phenomena like charge separation in Janus transition metal dichalcogenides-based van der Waals heterojunction materials. Covering latest state-of-the-art numerical simulations along with experimental results in the field, this review aims to provide a basic understanding of the tight relation between semiconductor nanomaterials and the proper simulation of their properties via surface hopping methods. Special stress is put on emerging state-ot-the-art techniques. By highlighting the challenge imposed by new materials, we depict emerging creative approaches, including high-level electronic structure methods and NA-MD methods to model nonadiabatic systems with high complexity. [ABSTRACT FROM AUTHOR]

In the Baeck-An (BA) approximation, first-order nonadiabatic coupling vectors are given in terms of adiabatic energy gaps and the second derivative of the gaps with respect to the coupling coordinate. In this paper, a time-dependent (TD) BA approximation is derived, where the couplings are computed from the energy gaps and their second time-derivatives. TD-BA couplings can be directly used in fewest switches surface hopping, enabling nonadiabatic dynamics with any electronic structure methods able to provide excitation energies and energy gradients. Test results of surface hopping with TD-BA couplings for ethylene and fulvene show that the TD-BA approximation delivers a qualitatively correct picture of the dynamics and a semiquantitative agreement with reference data computed with exact couplings. Nevertheless, TD-BA does not perform well in situations conjugating strong couplings and small velocities. Considered the uncertainties in the method, TD-BA couplings could be a competitive approach for inexpensive, exploratory dynamics with a small trajectories ensemble. We also assessed the potential use of TD-BA couplings for surface hopping dynamics with time-dependent density functional theory (TDDFT), but the results are not encouraging due to singlet instabilities near the crossing seam with the ground state.

Photosensitive azobenzene‐containing surfactants have attracted great attention in past years because they offer a means to control soft‐matter transformations with light. At concentrations higher than the critical micelle concentration (CMC), the surfactant molecules aggregate and form micelles, which leads to a slowdown of the photoinduced trans→cis azobenzene isomerization. Here, we combine nonadiabatic dynamics simulations for the surfactant molecules embedded in the micelles with absorption spectroscopy measurements of micellar solutions to uncover the reasons responsible for the reaction slowdown. Our simulations reveal a decrease of isomerization quantum yields for molecules inside the micelles. We also observe a reduction of extinction coefficients upon micellization. These findings explain the deceleration of the trans→cis switching in micelles of the azobenzene‐containing surfactants. [ABSTRACT FROM AUTHOR]

Recently, surface-hopping ab initio molecular dynamics (SH-AIMD) simulations have come to be used to discuss the mechanisms and dynamics of excited-state chemical reactions, including internal conversion and intersystem crossing. In dynamics simulations involving intersystem crossing, there are two potential energy surfaces (PESs) governing the motion of nuclei: PES in a spin-pure state and PES in a spin-mixed state. The former gives wrong results for molecular systems with large spin-orbit coupling (SOC), while the latter requires a potential gradient that includes a change in SOC at each point, making the computational cost very high. In this study, we systematically investigate the extent to which the magnitude of SOC affects the results of the spin-pure state-based dynamics simulations for the hydride MH 2 (M = Si, Ge, Sn, Pb) by performing SH-AIMD simulations based on spin-pure and spin-mixed states. It is clearly shown that spin-mixed state PESs are indispensable for the dynamics simulation of intersystem crossing in systems containing elements Sn and Pb from the fifth period onward. Furthermore, in addition to the widely used Tully's fewest switches (TFS) algorithm, the Zhu-Nakamura (ZN) global switching algorithm, which is computationally less expensive, is applied to SH for comparison. The results from TFS- and ZN-SH-AIMD methods are in qualitative agreement, suggesting that the less expensive ZN-SH-AIMD can be successfully utilized to investigate the dynamics of photochemical reactions based on quantum chemical calculations., (© 2023 Wiley Periodicals LLC.)

Fewest-switches surface hopping (FSSH) is employed in order to investigate the nonadiabatic excited-state dynamics of thiophene and related compounds and hence to establish a connection between the electronic system, the critical points in configuration space and the deactivation dynamics. The potential-energy surfaces of the studied molecules were calculated with complete active space self-consistent field and time-dependent density-functional theory. They are analyzed thoroughly to locate and optimize minimum-energy conical intersections, which are essential to the dynamics of the system. The influence of decoherence on the dynamics is examined by employing different decoherence schemes. We find that irrespective of the employed decoherence algorithm, the population dynamics of thiophene give results which are sound with the expectations grounded on the analysis of the potential-energy surface. A more detailed look at single trajectories as well as on the excited-state lifetimes, however, reveals a substantial dependence on how decoherence is accounted for. In order to connect these findings, we describe how ensemble averaging cures some of the overcoherence problems of uncorrected FSSH. Eventually, we identify carbon–sulfur bond cleavage as a common feature accompanying electronic transitions between different states in the simulations of all thiophene-related compounds studied in this work, which is of interest due to their relevance in organic photovoltaics. [ABSTRACT FROM AUTHOR]

We develop generalized polynomial chaos (gPC) based stochastic Galerkin (SG) methods for a class of highly oscillatory transport equations that arise in semiclassical modeling of non-adiabatic quantum dynamics. These models contain uncertainties, particularly in coefficients that correspond to the potentials of the molecular system. We first focus on a highly oscillatory scalar model with random uncertainty. Our method is built upon the nonlinear geometrical optics (NGO) based method, developed in Crouseilles et al. [Math. Models Methods Appl. Sci.23 (2017) 2031–2070] for numerical approximations of deterministic equations, which can obtain accurate pointwise solution even without numerically resolving spatially and temporally the oscillations. With the random uncertainty, we show that such a method has oscillatory higher order derivatives in the random space, thus requires a frequency dependent discretization in the random space. We modify this method by introducing a new "time" variable based on the phase, which is shown to be non-oscillatory in the random space, based on which we develop a gPC-SG method that can capture oscillations with the frequency-independent time step, mesh size as well as the degree of polynomial chaos. A similar approach is then extended to a semiclassical surface hopping model system with a similar numerical conclusion. Various numerical examples attest that these methods indeed capture accurately the solution statistics pointwisely even though none of the numerical parameters resolve the high frequencies of the solution. [ABSTRACT FROM AUTHOR]

The strong coupling regime between confined light and organic molecules turned out to be promising in modifying both the ground state and the excited states properties. Under this peculiar condition, the electronic states of the molecule are mixed with the quantum states of light. The dynamical processes occurring on such hybrid states undergo several modifications accordingly. Hence, the dynamical description of chemical reactivity in polaritonic systems needs to explicitly take into account the photon degrees of freedom and nonadiabatic events. With the aim of describing photochemical polaritonic processes, in the present work, we extend the direct trajectory surface hopping scheme to investigate photochemistry under strong coupling between light and matter. [ABSTRACT FROM AUTHOR]

Simulating the dynamics of a molecule initiated in an excited electronic state constitutes a rather challenging task for theoretical and computational chemistry, as such dynamics leads to a strong coupling between nuclear motion and electronic states, that is, a breakdown of the Born–Oppenheimer approximation. This New Views article proposes a brief overview on recent theoretical developments aiming at simulating the excited-state dynamics of molecules – nonadiabatic molecular dynamics – focusing in particular on strategies employing travelling basis functions to portray the dynamics of nuclear wavefunctions. We start by discussing the central equations for nonadiabatic molecular dynamics in a Born–Huang representation. We then propose a comparison between two commonly employed strategies to simulate the excited-state dynamics of molecular systems in their full configuration space, Ab Initio Multiple Spawning (AIMS) and Trajectory Surface Hopping (TSH). The equations of motion for the two techniques are compared and used to contrast their respective description of phenomena involving the decoherence of nuclear wavepackets. Some recent works and developments of the AIMS method are then summarised. This New Views article ends with a highlight on the Exact Factorisation of the molecular wavefunction and how this approach contrasts with the more conventional Born–Huang picture when it comes to the description of photophysical and photochemical processes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Simulations predict Aspirin and Ibuprofen as photostable, showing fast decay to S 0. • Carprofen and Suprofen show ultrafast decay to T 1 , with Φ T close to 1. • Indomethacin experiences trapping of the population in the S 1 state. Abstract Here we present a computational investigation of the excited state dynamics of 5 different active medical substances (aspirin, ibuprofen, carprofen, suprofen, indomethacin) which belong to the family of nonsteroidal anti-inflammatory drugs (NSAIDs). The nonadiabatic dynamics simulations were performed using the surface hopping method, with electronic energies and couplings evaluated on the fly in a semiempirical framework. For aspirin, the solvent decay dynamics was also considered by inserting it in a cluster of water molecules, following a QM/MM scheme. A quite diverse behavior was observed for the systems considered, going from fast deactivation to the S 0 (aspirin and ibuprofen), to ultrafast intersystem crossing to the triplet manifold (carprofen and suprofen), or to the generation of long lived S 1 states (indomethacin). To our knowledge, this is the first computational study of the photodynamics of these NSAIDs. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Surface hopping AIMD simulations clarified nonadiabatic dynamics for the dissociative recombination of CH 3 +. • In direct process, 96% of trajectories lead to CH 2 + H. • In indirect process via Rydberg state, the branching ratio approaches to the experimental one. • Indirect process also contributes to the DR even when direct process is possible. Abstract Ab initio molecular dynamics (AIMD) simulations were carried out to investigate dynamics in the dissociative recombination of CH 3 + at the state-averaged complete active space self-consistent field (SA-CASSCF) level. Nonadiabatic transitions between adiabatic electronic states were taken into account by the Tully's fewest switches algorithm. The direct process was examined by trajectories starting from the crossing points of the potential energy surfaces of the CH 3 + ground state and CH 3 dissociative state, while the indirect process was investigated by trajectories starting from the approximate crossing points of the CH 3 Rydberg state and dissociative states. It is shown that, in the direct process, the dominant products, CH 2 + H, are generated in 96% of trajectories, while in the indirect process, the ratio of the other products, CH + 2H, CH + H 2 , C + H 2 + H, increases extensively due to the intramolecular energy redistribution while descending through multiple potential energy surfaces, which is more consistent with the experimental observation. [ABSTRACT FROM AUTHOR]

The photoisomerization of all‐trans retinal in channelrhodopsins triggers the opening of a cation channel in the membrane of certain green algae. The stimulus resulting from cell depolarization enables the algae to perceive and react to the present lighting conditions. This property makes channelrhodopsins especially interesting for neuroscientific applications in optogenetics. We investigate the initial photoreaction in the channelrhodopsin chimera C1C2 with a combined quantum mechanical/molecular mechanical (QM/MM) strategy. For geometry optimizations, the OM3/RHF and OM3/MRCI/Amber protocols are used. Trajectory surface hopping calculations are performed with OM3/MRCI/Amber and a statistically relevant number of molecules to obtain reaction rates and quantum yields. The utilized models include a direct hydrogen bond of the retinal Schiff base to the proposed counterions in C1C2, i. e. either toward glutamate or aspartate. Static and dynamic aspects are compared to experimental findings including time constants and spectral traces. The calculations provide a rationale for the observed short and long time components in the photokinetics of C1C2 and yield detailed insight into the photoreaction mechanisms that include bicycle pedal and hula twist motions. The photoconversion of retinal in the channelrhodopsin chimera C1C2 was investigated with excited state molecular dynamics simulations applying the semiempirical OM3/MRCI approach and the Amber force field. The computations indicate a crossing of the S1 and S2 states, enabling population of the HOMO2→LUMO2 state. Short and long time components in the photokinetics of C1C2 are identified that are compatible with experimental findings. The molecules decay via two different reaction mechanisms involving hula twist and bicycle pedal motions. [ABSTRACT FROM AUTHOR]

Surface hopping algorithms are popular tools to study dynamics of the quantum-classical mixed systems. In this paper, we propose a surface hopping algorithm in diabatic representations, based on time dependent perturbation theory and semiclassical analysis. The algorithm can be viewed as a Monte Carlo sampling algorithm on the semiclassical path space for a piecewise deterministic path with stochastic jumps between the energy surfaces. The algorithm is validated numerically and it shows good performance in both weak coupling and avoided crossing regimes [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Aimed at filling the gap in the theoretical studies of the CH 3 's photo-dissociation. • Our results look promising reproducing the same trend as state of the art experiments. • The method used allows the interpretation of the internal mechanisms of the process. Abstract The photodissociation dynamics of methyl radical from selected vibrational levels of the 3 s and 3 p z Rydberg states has been studied using the trajectory surface hopping method on one-dimensional potential energy curves along the carbon-hydrogen dissociative coordinate and the non-adiabatic couplings between them, calculated by ab initio methods. Lifetimes and product distributions have been obtained for all the studied vibrational levels and compared with previous theoretical and experimental works. The theoretical lifetimes tend to decrease as vibrational excitation increases in accordance with experimental results. The agreement, however, is only qualitative considering the reduced dimensionality of the model. [ABSTRACT FROM AUTHOR]

Abstract The radiationless decay of the isothiazole and thiazole molecules in the gas phase is investigated by a combination of static MS-CASPT2 computations with dynamics simulations, and some deactivation pathways are identified leading from the lowest excited singlet (S 1 ) state back to the electronic ground (S 0 ) state. The dominant relaxation pathway of the excited isothiazole is found to involve out-of-plane ring deformation (ring puckering) at the C4=C5(H8) S1 moiety, while the excited-state decay of thiazole can proceed through the ring puckering and S1 C2 bond cleavage pathways both of which happen at the S1 C2(H6) = N3 moiety. On the basis of the calculation results, we suggest that both ring-puckering and ring-opening routes should play rather important roles in the photophysics and photochemistry of heterocyclic molecules, and the position of the N atom in the heterocyclic ring has an effect on the excited state deactivation. Graphical abstract Image 1 Highlights • Both ring-puckering and ring-opening play important roles in photophysics and photochemistry of heterocyclics. • The N atom position in the pentacyclic ring of isothiazoles and thiazoles has an effect on the excited state deactivation. • Nonadiabatic dynamics simulations are indispensable tools to give insights into radiationless deactivation mechanisms. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Surface hopping photodynamics simulations have been performed on a cluster of thymine interacting with six water molecules (T(H 2 O) 6). The second-order algebraic diagrammatic construction method (ADC(2)) has been used for calculating the required electronic energies and excited state gradients. Comparison with the previously performed photodynamics for the isolated thymine (Molecules 21 (2016) 1603) shows a similar global behavior and the central role of the S 1 (n π∗) minimum for further long-term dynamics. The main difference comes from the destabilization of the n π∗ state by hydrogen bonding, which leads to a significantly enhanced conversion rate from the bright S 2 (ππ∗) state to S 1 (n π∗) for the T(H 2 O) 6 cluster. On the other hand, the decay time to S 0 and the trapping in S 1 is significantly increased. Due to the localized character of the lone pair orbital involved in the n π∗ transition at one oxygen atom, specific changes in the structure of the hydrogen bonded network are observed. Since the hydrogen bonding of the water molecules connected to that oxygen atom is specifically weakened, they show dissociations from thymine during the photodynamics, starting within 30 fs after electronic excitation of thymine. [ABSTRACT FROM AUTHOR]

We consider a set of linear hyperbolic equations coupled by a linear source term and introduce a surface hopping Gaussian beam method as its numerical solver. The Gaussian beam part is basically classic, while the surface hopping part is derived from the equations. The whole algorithm shows high efficiency and good parallelizability. An application on the quantum-classical Liouville equations is presented to show its potential use in practice. [ABSTRACT FROM AUTHOR]

Electronically non-adiabatic processes are essential parts of photochemical process, collisions of excited species, electron transfer processes, and quantum information processing. Various non-adiabatic dynamics methods and their numerical implementation have been developed in the last decades. This review summarizes the most significant development of mixed quantum-classical methods and their applications which mainly include the Liouville equation, Ehrenfest mean-field, trajectory surface hopping, and multiple spawning methods. The recently developed quantum trajectory mean-field method that accounts for the decoherence corrections in a parameter-free fashion is discussed in more detail. [ABSTRACT FROM AUTHOR]