MRCPP-2.0 wishlist

[stigrj]

Dear 🤶

Please edit and add new features at will.

• make FunctionTree copyable
• introduce callable projectors and operators that return new FunctionTree
• switch to absolute precision measure rather than relative
• incorporate 4*pi into Poisson and Helmholtz operators
• MPI distributable FunctionTree
• 6D capabilities?

Import from MRChem:

• complex functions
• tensor operators and extend to functions?
• fast addition/rotation
• fast exchange