Shadow Molecular Dynamics and Atomic Cluster Expansions for Flexible Charge Models

J Goff and Y Zhang and C Negre and A Rohskopf and AMN Niklasson, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 19, 4255-4272 (2023).

DOI: 10.1021/acs.jctc.3c00349

A shadowmolecular dynamics scheme for flexible charge models ispresented where the shadow Born-Oppenheimer potential is derivedfrom a coarse- grained approximation of range-separated density functionaltheory. The interatomic potential, including the atomic electronegativitiesand the charge-independent short-range part of the potential and forceterms, is modeled by the linear atomic cluster expansion (ACE), whichprovides a computationally efficient alternative to many machine learningmethods. The shadow molecular dynamics scheme is based on extendedLagrangian (XL) Born-Oppenheimer molecular dynamics (BOMD)Eur. Phys. J. B 2021, 94, 164. XL-BOMD provides stable dynamics while avoiding the costlycomputational overhead associated with solving an all-to-all systemof equations, which normally is required to determine the relaxedelectronic ground state prior to each force evaluation. To demonstratethe proposed shadow molecular dynamics scheme for flexible chargemodels using atomic cluster expansion, we emulate the dynamics generatedfrom self-consistent charge density functional tight-binding (SCC-DFTB)theory using a second-order charge equilibration (QEq) model. Thecharge-independent potentials and electronegativities of the QEq modelare trained for a supercell of uranium oxide (UO2) anda molecular system of liquid water. The combined ACE+XL-QEq moleculardynamics simulations are stable over a wide range of temperaturesboth for the oxide and for the molecular systems and provide a precisesampling of the Born-Oppenheimer potential energy surfaces.Accurate ground Coulomb energies are produced by the ACE-based electronegativitymodel during an NVE simulation of UO2, predicted to bewithin 1 meV of those from SCC- DFTB on average during comparable simulations.

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