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GPAW \cite{gpaw} is a DFT code that uses the projector-augmented wave (PAW) technique \cite{Bl_chl_1994,Kresse_1999} and integrates with the atomic simulation environment (ASE) \cite{Bahn_2002}.   Helpful Open-source Research TOol for N-fermion systems (HORTON) has as a primary design goal ease of extensibility for researching new methods in \textit{ab initio} electronic structure theory.  JANPA \cite{Nikolaienko_2014} computes natural atomic orbitals from a reduced one-particle density matrix.  Massively Parallel Quantum Chemistry program (MPQC) \cite{Janssen95}  can compute Hartree-Fock energies and gradients, density functional theory energies and gradients, and second-order perturbation theory energies and gradients.  \paragraph{Helper Applications}