DAISpY: A Domain Assignment and Interface Solution in Python for Charge-Transfer Analysis

Understanding the spatial character of electronic excitations, in particular the distinction between local and charge-transfer. (CT) contributions, is essential in the analysis of excited-state phenomena. However, commonly used approaches often rely on method-specific representations or implicit partitioning schemes, limiting their reproducibility and transferability across electronic-structure frameworks.Domain Assignment and Interface Solution in pYthon (DAISpY, pronounced ”daisy”) presents a standalone and format-agnostic tool for domain-based charge-transfer. (CT) analysis of excited states. The method builds on a general representation of excited states in terms of configuration interaction CI-like amplitudes and aggregates their contributions into domain → domain CT matrices. Orbital contributions are assigned to user-defined spatial domains, enabling a direct and intuitive mapping of electron-hole redistribution between molecular fragments. The formalism consistently treats singles, pairs, and doubles excitations while preserving normalization and avoiding double counting.DAISpY is designed as a modular and reproducible analysis framework, supporting multiple input routes, including electronic-structure checkpoint files and portable data representations. The implementation is independent of any specific quantum chemistry package, ensuring broad applicability. PROGRAM SUMMARY Program title: DAISpY (Domain Assignment & Interface Solution in pYthon)CPC Library link to program files: https://doi.org/10.17632/mhpghs4jck.1Developer’s repository link: https://gitlab.com/pybest-edev/ct-analysisLicensing provisions: GNU General Public License 3Programming language: Python (3.10+) with a C++17 backendSupplementary material: Example datasets, tutorial notebooks, and user documentationNature of problem:The interpretation of electronic excited states in terms of spatial charge redistribution remains non-trivial, particularly when distinguishing local excitations from inter-fragment charge transfer. Standard approaches, such as orbital inspection, density differences, or population analyses, often depend on specific electronic-structure implementations and may lack a reproducible and transferable definition of CT character. Moreover, excited states expressed as configuration interaction CI-like expansions contain contributions from multiple excitation ranks, making it difficult to quantify how electron density moves between molecular fragments in a consistent and fragment-resolved manner across different computational workflows.Solution method:DAISpY provides a standalone framework for domain-based CT analysis by mapping CI-like excitation amplitudes onto user-defined spatial domains. Molecular orbitals are assigned to domains based on their atomic contributions, and excitation weights are accumulated into CT matrices. The method supports singles, pairs, and doubles excitations, with higher-order contributions consistently decomposed into effective one-electron channels to preserve normalization and avoid double counting. The implementation is modular and format-agnostic, supporting multiple input routes (HDF5 checkpoints or portable data directories) and offering CLI & Python API and a graphical interface for domain definition and analysis.Additional comments including restrictions and unusual features: DAISpY is independent of any specific quantum chemistry package and can process data from compatible electronic-structure workflows. Domain definitions are user-controlled and can be created interactively via a graphical interface or provided as labeled coordinate files, ensuring reproducibility. The results depend on the chosen orbital representation, active space, and domain partitioning, and should be interpreted in the context of the underlying electronic-structure method. A native C++ backend is used for performance-critical operations, while the Python layer provides flexibility and integration into automated workflows. The software supports both human-readable reports and spreadsheet-oriented outputs for further analysis.References:Interactive environment for testing the code without installation: https://mybinder.org/v2/gl/pybest-edev%2Fct-analysis/notebook?urlpath=%2Fdoc%2Ftree%2Ftutorial.ipynbS. Jahani, K. Boguslawski, P. Tecmer, The relationship between structure and excited-state properties in polyanilines from geminal-based methods, RSC advances. 13 (40) (2023) 27898–27911.L. Szczuczko, M. Gałyńska, M. H. Kriebel, P. Tecmer, K. Boguslawski, Domain-Based Charge-Transfer Decomposition and Its Application to Explore the Charge-Transfer Character in Prototypical Dyes, J. Chem. Theory Comput. 21 (9) (2025) 4506–4519.L. Szczuczko, J. Szczuczko, M. Gałyńska, K. Boguslawski, A Flexible, Automated, and Basis-Set-Insensitive Domain-Based Charge-Transfer Decomposition for Correlated Wave Functions and Its Application to Inter- and Intramolecular Cases, J. Phys. Chem. Lett. 17 (22) (2026) 6245–6255. PROGRAM SUMMARY Program title: DAISpY (Domain Assignment & Interface Solution in pYthon)CPC Library link to program files: https://doi.org/10.17632/mhpghs4jck.1Developer’s repository link: https://gitlab.com/pybest-edev/ct-analysisLicensing provisions: GNU General Public License 3Programming language: Python (3.10+) with a C++17 backendSupplementary material: Example datasets, tutorial notebooks, and user documentationNature of problem:The interpretation of electronic excited states in terms of spatial charge redistribution remains non-trivial, particularly when distinguishing local excitations from inter-fragment charge transfer. Standard approaches, such as orbital inspection, density differences, or population analyses, often depend on specific electronic-structure implementations and may lack a reproducible and transferable definition of CT character. Moreover, excited states expressed as configuration interaction CI-like expansions contain contributions from multiple excitation ranks, making it difficult to quantify how electron density moves between molecular fragments in a consistent and fragment-resolved manner across different computational workflows.Solution method:DAISpY provides a standalone framework for domain-based CT analysis by mapping CI-like excitation amplitudes onto user-defined spatial domains. Molecular orbitals are assigned to domains based on their atomic contributions, and excitation weights are accumulated into CT matrices. The method supports singles, pairs, and doubles excitations, with higher-order contributions consistently decomposed into effective one-electron channels to preserve normalization and avoid double counting. The implementation is modular and format-agnostic, supporting multiple input routes (HDF5 checkpoints or portable data directories) and offering CLI & Python API and a graphical interface for domain definition and analysis.Additional comments including restrictions and unusual features: DAISpY is independent of any specific quantum chemistry package and can process data from compatible electronic-structure workflows. Domain definitions are user-controlled and can be created interactively via a graphical interface or provided as labeled coordinate files, ensuring reproducibility. The results depend on the chosen orbital representation, active space, and domain partitioning, and should be interpreted in the context of the underlying electronic-structure method. A native C++ backend is used for performance-critical operations, while the Python layer provides flexibility and integration into automated workflows. The software supports both human-readable reports and spreadsheet-oriented outputs for further analysis.References:Interactive environment for testing the code without installation: https://mybinder.org/v2/gl/pybest-edev%2Fct-analysis/notebook?urlpath=%2Fdoc%2Ftree%2Ftutorial.ipynbS. Jahani, K. Boguslawski, P. Tecmer, The relationship between structure and excited-state properties in polyanilines from geminal-based methods, RSC advances. 13 (40) (2023) 27898–27911.L. Szczuczko, M. Gałyńska, M. H. Kriebel, P. Tecmer, K. Boguslawski, Domain-Based Charge-Transfer Decomposition and Its Application to Explore the Charge-Transfer Character in Prototypical Dyes, J. Chem. Theory Comput. 21 (9) (2025) 4506–4519.L. Szczuczko, J. Szczuczko, M. Gałyńska, K. Boguslawski, A Flexible, Automated, and Basis-Set-Insensitive Domain-Based Charge-Transfer Decomposition for Correlated Wave Functions and Its Application to Inter- and Intramolecular Cases, J. Phys. Chem. Lett. 17 (22) (2026) 6245–6255.