CM THEORY SEMINAR<br>Accurate Many-Body Methods for Electronic Structure of Large Systems

Accurate treatment of even simple chemical processes requires accuracy beyond that afforded by one-body methods. Many-body wave functions unfortunately suffer from slow convergence with the basis set size stemming from the effects of the electron-electron Coulomb singularity. Explicitly-correlated R12/F12 methods are practical means of analytic embedding of the proper (spin-dependent) cusps into the many-body wave function. Unlike the use of Jastrow factors in quantum Monte-Carlo, stochastic integration is completely avoided and the computational expense is similar to that of standard wave function methods, with greatly improved basis set convergence. I will discuss (1) the recent developments of the explicitly-correlated methods related to their application to large systems (hundreds of atoms) and (2) the use of explicit correlation for improved description of the self-energy in propagator-based many-body methods.