A fully direct RI-HF algorithm: Implementation, optimised auxiliary basis sets, demonstration of accuracy and efficiency

A direct HF algorithm using the resolution of identity for Coulomb and exchange integrals (RI-HF) was implemented within the program system TURBOMOLE. A variational procedure for the optimisation of auxiliary functions is presented as well as optimised auxiliary basis sets for large basis sets up to Br. The accuracy of RI-HF energies and of MP2 energies based on RI-HF wave functions is demonstrated for a large test set of molecules. Accuracy of first order properties is documented for selected cases. The size dependency of the RI errors and the efficiency of the method are investigated for closo-boranes [BnHn]2− (n = 4–12).