Phase Behavior of Water

Despite over 50 years since the first computer simulations of liquid water and numerous subsequent studies, achieving a realistic molecular-level understanding of water's properties across all phases has remained elusive. Over the past decade, efficient algorithms for correlated electronic structure calculations of small molecular complexes, combined with significant advances in machine-learned representations of multidimensional potential energy surfaces, have paved the way for the development of the MB-pol data-driven many-body potential. This potential is based on a rigorous representation of the many-body expansion of interaction energies. In this contribution, I provide a comprehensive overview of the performance of MB-pol, which enables realistic simulations of water—from gas-phase clusters to liquid water and ice. I focus specifically on water's phase behavior in the supercooled regime, identifying the elusive liquid-liquid critical point through realistic molecular simulations. Comparisons with experimental data across the water phase diagram demonstrate that MB-pol effectively captures water's molecular properties under diverse conditions, fulfilling the long-sought goal of a "universal model" of water.