Abstract: Neural networks (NNs) are extremely effective interpolators in atomistic simulations. Given abundant and diverse data, NN interatomic potentials (NNIPs) can be trained to replicate potential energy surfaces with the accuracy of high-level and high-cost electronic structure methods while reducing the computational cost by orders of magnitude. However, NNIPs are notoriously delicate and struggle to generalize to points outside the training data, which may result in highly erroneous predictions for atomic configurations not seen at train time. Naturally, the purpose of NNIP is to perform simulations at much larger time and length scales than can be accessed with the ground truth method, meaning that rare events not represented in the training data are likely to be seen in production. Uncertainty estimates then become key to building self-correcting NNIPs. By assigning confidence to their predictions during production simulations, the NNIPs can signal that the model is uncertain and needs to be re-trained with new data that is representative of the new environment, in so-called active learning strategies. However, this still requires (a cycle of) large-scale simulations to encounter these rare environments, identify new training data, and restart the process.

Here, we describe how NN uncertainty quantification methods based on both ensembles enable gradient-based active learning to systematically improve NN potentials. The uncertainty metrics are differentiable end-to-end with respect to model inputs, and directly distort input atomic positions towards regions of high uncertainty through gradient ascent methods. The geometries found are thus representative of high-uncertainty configurations, but they are visited through fast optimization methods, rather than waiting for a traditional simulation to visit them.

Bio: Rafael Gomez-Bombarelli (Rafa) is the Jeffrey Cheah Career Development Professor at MIT’s Department of Materials Science and Engineering since 2018. He received BS, MS, and PhD (2011) degrees in chemistry from Universidad de Salamanca (Spain).