Francesco Paesani University of California, San Diego (UCSD) Two of the most challenging problems at the frontier of contemporary electronic structure theory are the accurate representation of intermolecular interactions and the development of reduced-scaling algorithms applicable to large systems. To some extent, these two problems are antithetical, since the accurate calculation of noncovalent interactions typically requires correlated, post-Hartree–Fock methods whose computational scaling with respect to system size precludes the application to large systems. In this talk, I will describe our many-body molecular dynamics (MB-MD) methodology that overcomes these limitations and enables chemically accurate computer simulations from the gas to the condensed phase. MB-MD is a unified molecular dynamics framework that combines chemically accurate potential energy, dipole moment, and polarizability surfaces derived entirely from correlated electronic structure data using “active learning” techniques with quantum dynamical methods that explicitly account for nuclear quantum effects. The accuracy of our MB-MD methodology is assessed here through the analysis of the properties of water from the gas to the condensed phase with a particular emphasis on nuclear quantum effects and vibrational spectroscopy.