Parallel Two-Electron Reduced Density Matrix Based Electronic Structure Software for Highly Correlated Molecules and Materials

Variational two-electron reduced-density-matrix (v2RDM) methods can provide a reference-independent description of the electronic structure of many-electron systems that naturally captures multireference correlation effects. These methods offer one of the few possible routes to performing the large-active-space computations that are necessary for the qualitative description of strongly-correlated molecules and materials. However, existing implementations of the v2RDM method exhibit a time-to-solution that is often prohibitively large for the general description of extended molecules. We are developing a parallel implementation of the v2RDM approach within the Q-Chem quantum chemistry package. We have implemented two- and three-particle N-representability conditions that are generalized to treat both closed- and open-shell systems, and we have interfaced our v2RDM solver with an orbital optimization procedure, thereby achieving a v2RDM-driven complete active space self-consistent field procedure. We will improve the parallel performance of our algorithms and expand the functionality of our software, fully integrating it with the useful features available in Q-Chem, including effective core potentials, methods for incorporating solvent effects, and analytic gradient evaluation. Our final software product will also include v2RDM-based approaches for the treatment of dynamical electron correlation and electronically excited states.