Resolution of the identity approximation applied to PNOF correlation calculations

In this work, the required algebra to employ resolution of identity approximation within Piris Natural Orbital Functional (PNOF) is developed, leading an implementation named DoNOF-RI. The arithmetic scaling reduced from fifth-order fourth-order, and memory fourth-order third-order, allowing significant computational time savings. After DoNOF-RI calculation has fully converged, a restart with four-center electron repulsion integrals can be performed remove effect auxiliary basis set incompleteness, quickly converging exact result. proposed approach been tested on cycloalkanes other molecules general interest study numerical results as well speed-ups achieved by PNOF7-RI when compared PNOF7.