A new efficient approach to the direct restricted active space self-consistent field method

We present an implicitly parallel method for integral-block driven restricted active space self-consistent field (RASSCF) algorithms. Our algorithm entirely avoids testing the index space for nonzero contributions to the CI vector, by finding entire blocks of contributions through use of simple algebraic rules (propagation rules). The blocks themselves are efficiently identified by introducing a RAS model space. Our algorithm is capable of making efficient use of modern supercomputer hardware, supporting both shared and distributed memory architectures and hybrids. Applicability of our method is demonstrated with a RASSCF investigation of the first two excited states of indole.