About Newton-X 26

About Newton-X 26

Newton-X is an open-source software platform for mixed quantum–classical dynamics (MQCD) simulations of excited-state molecular processes.

In MQCD, nuclear motion is described by classical trajectories, while electronic populations evolve quantum-mechanically via nonadiabatic transitions.

Newton-X 26 provides complete workflows for these simulations, from initial-condition preparation to trajectory propagation and postprocessing/archiving.

A workflow-oriented platform

Newton-X 26 is organized around the three core steps common to MQCD projects:

    1. Spectra and initial conditions.
      MQCD is ensemble science: meaningful observables require many trajectories. Newton-X, therefore, treats initial-condition preparation as a first-class workflow component, combining phase-space sampling with spectral screening to select which geometries initiate dynamics on chosen electronic states. These steps are implemented in NX-CS, which also enables simulations of nuclear-ensemble spectra.
    2. Dynamics simulations.
      Trajectory propagation is typically the dominant cost and the key modeling choice: which MQCD strategy best matches the target observables at an affordable electronic-structure level. Newton-X 26 supports multiple propagation paradigms within the same platform, including:
      – surface hopping (NX-NS),
      – decoherence-corrected Ehrenfest dynamics (Skitten)
      – ab initio multiple spawning (Legion).
      Optional machine-learning acceleration is provided through MELTS.
    3. Analysis, postprocessing, and archiving.
      Extracting physics from raw trajectories requires careful consolidation, statistical analysis, and reproducible reporting. Newton-X 26 integrates with Ulamdyn for advanced trajectory analysis, including unsupervised learning.

What is distinctive in Newton-X 26

Surface hopping as a configurable family

Newton-X offers instantaneous hopping schemes that explicitly propagate electronic amplitudes (including fewest-switches surface hopping and local-diabatization surface hopping), as well as global/asymptotic schemes such as Landau–Zener surface hopping.

Newton-X supports different velocity-adjustment options to enforce energy conservation. It can also apply decoherence corrections (simplified decay of mixing and overlap-based decoherence) to schemes where electronic coefficients are available.

Multiple coupling routes

Newton-X 26 supports three practical routes to nonadiabatic couplings, chosen to match what an electronic-structure method can actually provide.

    • Nonadiabatic coupling vectors (NACVs) when they are available from the electronic-structure method.
    • Wavefunction overlaps, which enable time-derivative couplings (TDCs) and also support local diabatization when explicit NACVs are unavailable.
    • Curvature-based approaches, including Landau–Zener-type estimates and the time-dependent Baeck–An (TD-BA) approximation, offer low-cost alternatives that rely on energy gaps and their time derivatives.

Ehrenfest dynamics with built-in decoherence via SLED

For mean-field dynamics, Newton-X offers Ehrenfest dynamics with spontaneous localization (SLED).

SLED introduces stochastic localization/decoherence terms so that each trajectory evolves with continuous decoherence in the adiabatic basis, while at the ensemble level it corresponds to a Lindblad-type reduced-density-matrix evolution.

Highly flexible AIMS algorithm

Newton-X includes AIMS, based either on NACVs or TDCs (via TD-BA). This broadens the range of electronic-structure methods that can be coupled to AIMS when explicit NACVs are difficult or unavailable.

Gaussian parameters are available across the entire periodic table.

Interfaces and electronic-structure connectivity

Newton-X is driven by on-the-fly electronic-structure calculations of energies, gradients, and couplings. The platform connects to multiple third-party electronic-structure engines via NX-Interfaces, with electronic states ranging from CASPT2 to TDA based on semiempirical xTB references.

What Newton-X 26 is for

Taken together, Newton-X 26 aims to couple methodological breadth (multiple MQCD paradigms) with transparent, reproducible workflows and an ecosystem suitable for both routine applications and method development.

Citing Newton-X

Please cite Newton‑X as:

    • Barbatti, M.; Bondanza, M.; Crespo‑Otero, R.; Demoulin, B.; Dral, P. O.; Granucci, G.; Kossoski, F.; Lischka, H.; Mennucci, B.; Mukherjee, S.; Pederzoli, M.; Persico, M.; Pinheiro Jr, M.; Pittner, J.; Plasser, F.; Sangiogo Gil, E.; Stojanovic, L. Newton‑X Platform: New Software Developments for Surface Hopping and Nuclear Ensembles. J. Chem. Theory Comput.  2022,  18, 6851–6865. DOI: 10.1021/acs.jctc.2c00804

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References for specific methods, algorithms, and third‑party programs used in Newton‑X are provided in the documentation.

Legacy programs and backward compatibility

Newton-X 26 includes the earlier surface-hopping programs to support legacy inputs and to facilitate reproduction of published results. These legacy executables are frozen: they will not receive new features and are not actively supported. Users are therefore strongly encouraged to adopt the Newton-X 26 workflows for new simulations.

Contact Newton-X

Aix Marseille University, CNRS, Institut de Chimie Radicalaire
52 Av Esc. Normandie Niemen
13397 Marseille cedex 20
France

Email: info@newtonx.org

For technical questions, bug reports, and user support, please use the Newton-X discussion group (support is not handled by email).