DAISpY: A domain assignment and interface solution in pYthon for charge-transfer analysis
Description
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.