Fitting that is compatible with ab initio electronic-structure calculations is defined.
Robust fits affect the total energy only in second and higher orders of the error due to fitting.
Variational fits guarantee that self-consistent energies decrease if orbital basis sets are augmented in any way. Robust and variational fitting of charge distributions is described, and its proper implementation in ab initio electronic-structure calculations discussed. Analytic, robust and variational fitting of the cube root of the charge density is described. Parallelization work is currently underway in collaboration with ARL CISD using the OpenMP programming model and a variety of MSRC resources. Supported by the Office of Naval Research directly and through the Naval Research Laboratory.