Linear-scaling calculation of experimental observables for molecular augmented dynamics simulations

Abstract

Aligning theoretical atomistic structural models of materials with available experimental data presents a significant challenge for disordered systems. The configurational space to navigate is vast, and faithful realizations require large system sizes with quantum-mechanical accuracy in order to capture the distribution of structural motifs present in experiment. Traditional equilibrium sampling approaches offer no guarantee of generating structures that coincide with experimental data for such systems. An efficient means to search for such structures is molecular augmented dynamics (MAD) [arXiv:2508.17132], a modified molecular dynamics method that can generate ab-initio accurate, low-energy structures through a multi-objective optimization of the interatomic potential energy and the experimental potential. The computational scaling of this method depends on both the scaling of the interatomic potential and that of the experimental potential. We present the general equations for MAD with linear-scaling formulations for calculating and matching X-ray/neutron diffraction and local observables, e.g., the core-electron binding energies used in X-ray photoelectron spectroscopy. MAD simulations can both find metastable structures compatible with non-equilibrium experimental synthesis and lower energy structures than alternative computational sampling protocols, like the melt-quench approach. In addition, generalizing the virial tensor with the experimental forces enables generalized barostatting, allowing one to find structures whose density matches that compatible with the experimental observables. Scaling tests with the TurboGAP code demonstrate their linear-scaling nature for both CPU and GPU implementations, the latter of which has a 100$\times$ speedup compared to the CPU.