Psi4
An open-source molecular quantum chemistry engine with a C++ core and Python driver, including DFT, correlated methods and SAPT interaction analysis.
Where it fits
Automated molecular calculations and noncovalent-interaction analysis in Python workflows.
Limits and practical considerations
Check method-specific derivative, memory and parallelization support before scaling a workflow.
Licensing and access
LGPL-3.0; the project explicitly encourages education, research and industry use.