(388b) A Novel Route to Phase Diagrams: Recovering 0 Kelvin Hamiltonian Parameters from High-Temperature Disordered Phases

Effective Hamiltonians, when used in tandem with statistical mechanics techniques, offer a rigorous connection between 0 Kelvin ab-initio simulations and finite temperature experimental observations. Specifically, cluster expansion Hamiltonians can extrapolate the complex, many-body electron problem of density functional theory into a series of simple site-wise basis functions (e.g., products of site coccupany variables) on an atomic scale. The resulting energy polynomial is computationally inexpensive, and hence suitable for the (tens of) thousands of calculations of thousand-site systems required by stochastic methods. We present a new method to run a cluster expansion "in reverse", using high-temperature observations and thermodynamic connections to predict the 0 Kelvin energy spectrum and associated ground states. By re-examining the cluster expansion formalism through the lens of entropy-maximization approaches, we develop an algorithm to select clusters and determine cluster interactions using only a few, high-temperature experiments on disordered phases. In this talk, we will develop our formalism and demonstrate multiple success using our approach. Specifically, we have explored three systems: two synthetic model Hamiltonians developed on a 2D triangular lattice, and an Au-Cu-like system in a 3D FCC lattice. In all cases, our new method can recover not only the stable ground states at 0 Kelvin, but also the full phase behavior through all of composition-temperature space.