CFOUR
A high-level molecular quantum-chemistry suite centered on coupled-cluster methods, analytic derivatives and accurate spectroscopic properties.
Where it fits
Small-molecule benchmark energetics, vibrational spectroscopy and correlated response properties.
Limits and practical considerations
High-order correlation grows expensive quickly; check supported references and derivatives for each method.
Licensing and access
No charge for non-commercial use after signing a licence agreement; this is not an unrestricted open-source grant.
Official documentation and project