Photochemical processes span time scales from femtoseconds to nanoseconds, and their simulation via fewest-switches surface hopping (FSSH) requires a large number of computationally expensive electronic structure evaluations. Machine learning (ML) interatomic potentials can reduce this cost; however, they must be trained on data sets that capture the most relevant regions of configurational space. We present MELTS, a fully automated active learning (AL) program for FSSH that iteratively improves ML models by using trajectory propagation to guide sampling. MELTS integrates Newton-X and MLatom through socket-based communication, minimizing I/O overhead and enabling large-scale simulations with a user-friendly interface. We validate the AL protocol implemented in MELTS on two contrasting systems: ultrafast fulvene dynamics (tens of femtoseconds) and nanosecond-scale pyrene fluorescence. In both cases, MELTS delivers quantitative agreement with reference quantum results while reducing computational time by up to 3 orders of magnitude. This demonstrates that MELTS can efficiently generate accurate ML potentials for photochemical processes across a wide range of time scales.

Nonadiabatic couplings (NACs) play a crucial role in modeling photochemical and photophysical processes with methods such as the widely used fewest-switches surface hopping (FSSH). There is, therefore...

Nonadiabatic molecular dynamics simulations provide a theoretical understanding of various excited-state processes in photochemistry, offering access to band widths, radiative or nonradiative relaxation and corresponding lifetimes, excited-state energies, and charge transfer. The range of method developments within the framework of time-dependent density functional theory is exceedingly large for molecular quantum chemistry. Still, it shrinks significantly when aiming to treat periodic boundary conditions. To address this gap and complement existing software packages for solid-state nonadiabatic molecular dynamics, we present an interface between the CP2K electronic structure and the NEWTON-X surface hopping codes. The interface features the generation of initial conditions, as well as adiabatic and nonadiabatic molecular dynamics, based on phenomenological or numerical time-derivative couplings. Setups are validated on gas-phase pyrazine, with electronic absorption spectra and excited-state populations for transitions between the lowest singlet states being in agreement with established molecular quantum chemistry methods. Extending the system size to crystalline pyrazine, limitations of approximate couplings are discussed, and the efficiency and applicability of the interface are demonstrated by computing broad spectra over several eV and 100 fs trajectories, considering couplings between all 80th lowest excited states, at low computational cost with a mixed semiempirical density functional theory setup.

Paracyclophanes are rigid, three-dimensional frameworks in which two benzene rings are held in a parallel, stacked arrangement by short aliphatic linkers. Their derivatives display pronounced through-...

Photoacids exhibit an increase in acidity upon electronic excitation, providing powerful tools for studying excited-state proton transfer (ESPT) reactions. While these photoacids have been used extens...

We propose Ehrenfest Dynamics with Spontaneous Localization (SLED), a decoherence-corrected extension of Ehrenfest dynamics based on the Gisin-Percival quantum-state diffusion (QSD) equation. In SLED,...

This paper proposes a method to simulate nonadiabatic dynamics initiated by thermal light, including solar radiation, in the frame of mixed quantum-classical (MQC) methods, like surface hopping. The m...

The COLUMBUS program system provides the tools for performing high-level multireference (MR) computations, including the multireference configuration interaction (MRCI) method and its multireference a...

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For decades, computational theoretical chemistry has provided critical insights into molecular behavior, often anticipating experimental discoveries. This review surveys twenty notable examples from t...