An approach to the systematic neglect of the small-in-value electron repulsion integrals which is used in a number of approximate self-consistent field molecular orbital schemes. It means that all the products of atomic orbitals \(\upchi_{\upmu} \upchi_{\upnu}\) are set to zero and the overlap integral \(\rm{S}_{\upmu\upnu} = \updelta_{\upmu\upnu}\) (where \(\updelta_{\upmu\upnu}\) is the Kronecker delta). The ZDO approximation greatly simplifies the computation of wavefunctions by eliminating many of two-electron integrals. At the ZDO approximation all three- and four-centered integrals vanish.