The multi-reference configuration interaction method on massively parallel architectures

We report on a scalable implementation of the configuration- selecting multi-reference configuration interaction method for massively parallel architectures with distributed memory. Based on a residue driven evaluation of the matrix elements this approach allows the routine treatment of Hilbert spaces of well over 109 determinants as well as the selective treatment of triple and quadruple excitations with respect to the reference space. We demonstrate the scalability of the method for up to 128 nodes on the IBM-SP2. We elaborate on the specific adaptation of the transition residue-based matrix element evaluation scheme that ensures the scalability and load-balancing of the method and discuss the projects using this methodology that axe presently under investigation: the elucidation of electronic dynamics near the conical intersection of NO2, the calculation of potential energy surfaces and electronic spectra of transition metal compounds such as Cr2 and the first row transition metal dihalides, the investigation of the electronic structure of aromatic compounds such as benzene, naphtalene and anthrazene and their derivatives and the ab-initio determination of microscopic spin- and spin-phonon coupling constants in quasi-onedimensional transition metal compounds, such as CuGeO3 and NaV2O5 in the solid state.