It has recently been shown that the ab initio anharmonic free energy of fcc crystals can be approximated to meV/atom accuracy by a lattice of anharmonic nearest-neighbor bonds, where the bonding potential can be efficiently parametrized from the target system. We develop a mean-field approach for the free energy of a general bond lattice, analytically accounting for strong bond-bond correlations while enforcing material compatibility and thermodynamic self-consistency. Applying our fundamentally anharmonic model to fcc crystals yields free energies within meV/atom of brute force thermodynamic integration for core seconds of computational effort. Potential applications of this approach in computational materials science are discussed.
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Acknowledgments. T.D.S. acknowledges support from the Agence Nationale de Recherche via the MEMOPAS project ANR-19-CE46-0006-1 and access to IDRIS HPC resources under the allocation A0070910965 attributed by GENCI. G.S. acknowledges support from NSF Grant No. DMS1818726, M.L. acknowledges support from NSF Grant 1906129, P.P. acknowledges support from ARO Grant W911NF-19-1-0243, and J.J. and J.N. acknowledge financial support by the German Research Foundation (DFG) through projects 405621217 and 405621160. All authors gratefully thank the Institute of Pure and Applied Mathematics at the University of California, Los Angeles for providing a stimulating environment during their long program “Complex Processes in High Dimensional Energy Landscapes”.