OCTOPUS

Octopus is a scientific program aimed at the ab initio virtual experimentation on a hopefully ever increasing range of systems types. Electrons are described quantum-mechanically within the Density-Functional Theory (DFT), in its time-dependent form (TDDFT) when doing simulations in time. Nuclei are described classically as point particles. Electron-nucleus interaction is described within the Pseudopotential approximation.

Octopus is free software, released under the GPL license, so you are free to use it and modify it.