Construction of Bituminous Coal Structure via a Molecular Dynamics-Coupled Hybrid Reverse Monte Carlo Approach

Bituminous coal is structurally disordered and chemically heterogeneous, which complicates atomistic construction when models are assembled from representative structural fragments or constrained by limited measurements. Using demineralized, vacuum-dried Shenmu bituminous coal, we developed a molecular dynamics-coupled hybrid reverse Monte Carlo (MD-HRMC) workflow under ReaxFF to construct and validate a three-dimensional periodic atomistic CHONS model containing 10,001 atoms in a 45.6 Å cubic cell (atomic fractions: C 51.27%, H 41.38%, O 6.62%, N 0.53%, and S 0.21%). High-energy synchrotron X-ray total scattering provided an experimental pair distribution function (PDF) as the primary structural constraint, while a ReaxFF-based energetic term penalized chemically implausible local environments. A staged MD-HRMC annealing protocol yielded concurrent stabilization of the PDF misfit and the ReaxFF potential energy, and the resulting model reproduced the experimental PDF over 0-10 Å. An independent comparison with quantitative solid-state ¹³C NMR and XPS supported the constructed chemical structure, including an aromatic carbon fraction of f _a' = 0.612 compared with the NMR-derived value of 0.57, as well as the predominance of nonoxygenated carbon environments. The constructed structure further revealed medium-range organization characterized by small- to intermediate-sized aromatic domains, locally confined but poorly connected void space, and a dominant covalent skeleton coexisting with a disconnected fragment population. Mean-squared displacement analysis indicated clear dynamical heterogeneity within the model. The resulting model provides an experimentally constrained and chemically validated atomistic representation of Shenmu bituminous coal and may serve as a structurally grounded basis for future refinement of atomistic coal models and for exploring coal structure-behavior relationships at the molecular level.