26.4.6 Split Coulomb operator treatment of weak and strong pairs ATTENUATE

This method is still in development and has to be considered experimental. We document it here because we hate `undocumented features', but please, do yourself a favour and don't use it for the time being. If you get in trouble with it, we won't help you.

The method relies on the partitioning of the Coulomb operator into a rapidly decaying short range part containing the singularity and a smooth long range part. The integrals over both parts of the Coulomb operator are then treated separately. The short range integrals are obtained by transformation of the short range integrals in the AO basis, which is faster than the conventional transformation as more efficient screening is possible. The long range integrals are treated by a multipole expansion. In contrast to conventional multipole expansions, this expansion has an infinite radius of convergence. The method is available by replacing the LOCAL or MULTP card by the ATTENUATE card.

ATTENUATE,[key1=value],[key2=value2], $\ldots$

It does everything the MULTP card does (i. e., distant pairs are still treated by ordinary multipole expansion), plus it will enable the split Coulomb operator treatment of weak and strong pairs and select reasonable defaults. See section 22.5 for details. If you don't want distant pairs to be treated by ordinary multipole expansion, simply specify DISTPAIR=0 on the ATTENUATE card. Note that this method will only work in the context of integral-direct calculations.