Does a Large Scale ab Initio Hartree-Fock Calculation Give Chemical Accuracy?

In a large molecule like a protein, a numerical error of a total energy value in the HartreeEFock calculation may exceed the required absolute chemical accuracy, 0.01kcal/mol. We estimated numerical errors in a Fock matrix generation and diagonalization. In the present Fock matrix construction algorithm, an estimated numerical error of a total energy value is larger than the required chemical accuracy when a basis set size is more than several thousands. The numerical error can be decreased to less than the required chemical accuracy by the contrived algorithm that Fock matrix elements are generated by a partial summation technique.