Minimal basis sets, denoted DSBSenv, have been developed based on the segmented basis sets of Ahlrichs and co-workers for use as environmental basis set for the domain-specific basis set incremental scheme with the aim of decreasing the CPU requirements of the incremental scheme. The use of this minimal basis within explicitly correlated (F12) methods has been enabled by the optimization of matching auxiliary basis sets for use in density fitting of two-electron integrals and the resolution-of-the-identity. The accuracy of these auxiliary sets has been validated by calculations on a test set containing small- to medium-sized molecules. The errors due to density fitting are about two to four orders of magnitude smaller than the basis set incompleteness error of the DSBSenv orbital basis sets. Additional reductions in computational cost are tested with the reduced DSBSenv basis sets, where the highest angular momentum functions of the DSBSenv auxiliary basis sets have been removed. The optimized and reduced basis sets are used in the framework of the domain-specific basis set of the incremental scheme to decrease the computation time without significant loss of accuracy. The computation times and accuracy of the previously used environmental basis and that optimized in this work is validated with a test set of medium- to large-sized systems. The optimized and reduced DSBSenv basis sets decrease the CPU-time by about 15.4% and 19.4% compared to the old environmental basis and retains the accuracy in the absolute energy with a standard deviation of 0.99 and 1.06 kJ/mol, respectively.
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