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arXiv · 2610.18220

MINFF: A Family of Classical Force Fields for Minerals with Tunable Angle Terms

Michael Holmboe·Nathan Lavauzelle·Rogers E. Swai
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Abstract

Atomistic simulations of minerals are limited by the accuracy and transferability of the force field. We introduce MINFF, a force field family for layered and non-layered oxides and hydroxides of M being Si, Al, Fe, Mg, Ca, Ti, Li and F. MINFF has no M-O bond terms. Instead M-O distances follow from electrostatics and dispersion, while a single harmonic angle term on all M-O triplets controls coordination geometry. Metal charges are DDEC6 charges from reference mineral structures, and oxygen charges are assigned by nearest-neighbour charge smearing, covering basal, apical, hydroxyl and edge sites and sites adjacent to isomorphous substitutions. The oxygen Lennard-Jones parameters are based on the OPC3 water model and change by less than 5% when re-optimised per mineral, so compatibility with OPC3 and related ion-pair potentials is measured rather than assumed. Metal Lennard-Jones parameters were fitted to unit-cell metrics, bond distances and angles, both synchronously across more than 30 reference minerals (general, GMINFF) and for individual minerals (tailored, TMINFF), each at four angle force constants (0, 250, 500 and 1500 kJ/mol/rad^2). With angle terms, MINFF reproduces experimental unit-cells metrics to within 0.5% and atom-type distances and angles to within 0.7-1.4% and 0.1-0.4%, with Global Instability Index values as low as 0.11, below those of CLAYFF (0.34) and INTERFACE (0.21). A moderate angle constant reproduces the stiff in-plane and soft shear elastic constants of phyllosilicates and improves the Kaolinite librational bands, and in hydrated Na-Montmorillonite MINFF gives the lowest residual factor against the 2W 00l pattern of the models tested. The general and tailored sets at four angle stiffnesses give direct control over the transferability-fidelity trade-off. Topologies can be generated with the atom (MATLAB) and atomipy (Python) libraries and at www.atomipy.io.

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Michael Holmboe, Nathan Lavauzelle, Rogers E. Swai. 2026-10-13. MINFF: A Family of Classical Force Fields for Minerals with Tunable Angle Terms. https://arxiv.org/abs/2610.18220

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