Description:

The core QEq algorithm is implemented and tested, but the project now needs to be refined into a polished, stable, and well-documented crate for public consumption. This involves three key activities: finalizing a clean and ergonomic public API, writing comprehensive RustDoc documentation with clear examples, and adding high-level architectural documentation to guide future contributors and advanced users. Completing these tasks will ensure cheq is not just functional but also professional, accessible, and maintainable from day one.

Tasks:

• Phase 1: Finalize Public API and Library Structure

  • In src/lib.rs:
    • Define the library's public API exclusively through pub use statements, creating a flat and discoverable interface.
    • Ensure all internal implementation modules (math, etc.) are kept private to the crate (mod math; not pub mod math;).
    • Confirm that all essential types (QEqSolver, AtomView, Atom, Parameters, SolverOptions, CalculationResult, CheqError) are re-exported from the top level.
    • Review the public fields and methods of all exported structs to ensure they represent a minimal and stable API surface.

• Phase 2: Implement Comprehensive API Documentation (RustDoc)

  • Crate-Level Documentation: In src/lib.rs, add //! comments at the top of the file. This documentation should include:
    • A high-level overview of the Charge Equilibration (QEq) method and the purpose of the cheq library.
    • A clear, complete, and runnable "Quick Start" example demonstrating the primary use case (e.g., calculating charges for a water molecule).
    • Brief notes on the core concepts like QEqSolver, AtomView, and Parameters.
  • Public Item Documentation: Add /// comments to all public functions, structs, traits, enums, and their fields/methods.
    • Clearly document the purpose of each item (e.g., what QEqSolver::solve does).
    • Explain the parameters and return values, including all possible variants of CheqError.
    • Document the units for physical quantities in structs like ElementData (e.g., eV, Angstroms).
    • Provide small examples for key functions where applicable.
  • Verification: Run cargo doc --open --document-private-items to build and visually inspect the generated documentation, ensuring it is clear, professional, and free of broken links.

• Phase 3: Add High-Level Architectural Documentation

  • Create README.md:
    • Write a user-facing README.md at the project root. This should be a more concise version of the crate-level documentation, suitable for browsing on GitHub.
    • Include installation instructions (how to add cheq to Cargo.toml).
    • Add badges for CI status and crates.io version once released.