Overcoming Sampling Limitations Using Machine-Learned Interatomic Potentials: The Case of Water-in-Salt Electrolytes

Machine-learned interatomic potentials hold the promise to enable the modeling of highly concentrated liquids over meaningful time scales, far from reach for current ab initio electronic structure methods. Here we evaluate the performances of various MACE potentials in modeling a 21 m water-in-salt electrolyte based on lithium bis(trifluoromethanesulfonyl)imide. We test out-of-the-box foundation models, as well as both fine-tuning and from-scratch training strategies. Our simulations demonstrate that surrogate models allow us to overcome sampling limitations of ab initio molecular dynamics, reaching an excellent agreement with experimental observables such as the structure factor. We also demonstrate the benefit of fine-tuning a foundation model over training from scratch, in terms of data efficiency, but most importantly as a means to provide information regarding configurations hard to sample, such as short Li+-Li+ distances. Finally, we show that depending on the reference exchange-correlation functional, empirical dispersion correction schemes can be detrimental. All in all, our work shows that machine-learned interatomic potentials are a good fit for the modeling of highly concentrated electrolytes over long time scales.