PyQuante

If you're a scientist looking for a reliable and user-friendly tool to develop quantum chemistry methods, look no further than PyQuante. This suite of programs is both free and open source, providing a cost-effective and customizable solution. PyQuante is primarily written in Python, with key modules written in C to ensure quick processing times. While it may not be as speedy as Jaguar, NWChem, Gaussian, or GAMESS, PyQuante is designed with ease of understanding and modification in mind.

It's important to note that PyQuante isn't necessarily intended to function as a full-fledged quantum chemistry program. Instead, its aim is to provide a well-crafted set of tools that scientists can use to create their own programs without having to start from scratch. This approach saves time and resources, allowing for greater focus on the scientific task at hand.

If you opt for PyQuante, you'll be relying on a software package that's licensed and distributed under the BSD License. This ensures that you're free to use, modify, and distribute PyQuante's codebase as needed while respecting the original author's copyright. All in all, PyQuante is strong software that's worth considering if you're in the market for quantum chemistry solutions.