Auxilliary Basis Coulomb Fit (ii)
The number of 3-centre integrals is significantly smaller than the 4-centre integrals used in the conventional coulomb evaluation, but for large molecules additional screening is required.
We make use of the Schwarz inequality
- Where p and q are AO basis functions and u are the fitting functions. Since screening is applied on a shell basis, the maximal integrals for each shell quartet are stored.
- Using this screening, and exploiting the aggregate memory of a parallel machine, it is possible to hold a significant fraction of the 3-centre integrals in core.