What free quantum chemistry packages that have constrained DFT (CDFT) implemented? A google search does not reveal anything, perhaps there may exist a better resource to find the packages.

Can someone that works with CASTEP and VASP explain to me how a workflow might change between the two programs? I am very familiar with VASP but have not used CASTEP before. As an example, assuming we have an atomic model that is well defined (from a tool such as ASE) we can make a POSCAR file. ...