SymResponse

A unified framework for response theory at different levels of electronic-structure theory.

The theoretical background can be found in:

[1] Bin Gao and Magnus Ringholm, Unified Framework for Molecular Response Functions of Different Electronic-Structure Models, J. Phys. Chem. A 2025, 129, 3709-3721.

Reference [1] describes the computation of response functions by using

• Atomic orbital density matrix-based response theory
• Coupled-cluster response theory

[2] Bin Gao, Magnus Ringholm amd Kenneth Ruud, A unified framework for the application of response theory using different electronic-structure models, in manuscript 2026.

Reference [2] describes the computation of residues by using

• Atomic orbital density matrix-based response theory
• Coupled-cluster response theory
• Multi-configurational self-consistent field response theory

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License

SymResponse is licensed under the Mozilla Public License Version 2.0. See the LICENSE file for more information.

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Installation

SymResponse depends on the symbolic computation crate Tinned, and is a reimplementation of [1] using the Rust programming language.

The legacy C++ implementation can be found in the symrsp-cxx branch.

Build Rust library

cargo build -p symresponse_lib --release

or

cargo build-lib

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Documentation

The full API documentation can be generated with:

cargo doc -p symresponse_lib

To open it in a browser:

cargo doc -p symresponse_lib --open

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Examples

Examples of using the SymResponse crate can be found in the tests folder:

• cc_response.rs and cc_residue.rs demonstrate the computation of response functions and residues at the level of coupled-cluster response theory.
• dao_response.rs and dao_residue.rs demonstrate response function and residue computations within atomic orbital density matrix–based response theory.
• mcscf_response.rs and mcscf_residue.rs demonstrate response function and residue computations within multi-configurational self-consistent field (MCSCF) response theory.
• orb_cc_response.rs demonstrates response function computations within orbital-relaxed coupled-cluster response theory.

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C FFI

This project also provides a C-compatible interface in the symresponse_ffi crate, allowing the library to be used from C and other languages with FFI support.

See the symresponse_ffi README for usage details and examples.