Introduction

RustiQ is an experimental Rust quantum chemistry application and reusable rustiq-chem-core library. This manual serves scientific users, Rust contributors, and theoretical chemists.

Do not use RustiQ results for research conclusions without independent validation against established quantum chemistry packages.

Choose TOML for a single calculation or optional Nickel for parameterized studies. Both formats share the same defaults and validation; see calculation inputs and execution for how an input becomes a result.

Where should I start?

• Scientific users: Installation → First H₂ calculation → Interpreting output. These explain how to run the software without writing Rust. Read scientific limitations before using the results.
• Rust developers and architects: Development environments → Contributing, architecture, and the Rust API → Documentation checks. Start with the calculation lifecycle to see how input, scientific code, and reporting fit together. User-guide commands use the installed rustiq executable; a source checkout can install it with the instructions on the installation page or run it through Cargo.
• Theoretical chemists: First calculation → Reference comparisons → Scientific limitations. These identify tested evidence and current assumptions without requiring development tools. The release binary is sufficient for calculations; reproducing the reference suite additionally requires a source checkout and its documented test environment.

The glossary explains unfamiliar scientific and software terms. Existing workflow notes preserve useful operational guidance alongside the user guides and CLI reference.

Implemented capabilities include RHF, UHF, MP2, XYZ geometries, Gaussian basis sets, TOML and native Nickel input, sequential studies, and versioned JSON. The practical user guides now cover these capabilities, including HF/MP2 calculations, Nickel studies, JSON output, and portable calculation bundles. The command-line reference describes the shipped commands and options.

Portable .rustiq bundles can be written, reused, and inspected from the CLI as well as through Rust APIs. Start with the portable bundle guide for a runnable CLI workflow, then see the persistence specification for the archive contract. The authoritative references page links to the roadmap for plans and to the files that define existing contracts.