Recorded 29 March 2022. Christoph Ortner of the University of British Columbia presents "Modelling Atomic Properties with the Atomic Cluster Expansion" at IPAM's Multiscale Approaches in Quantum Mechanics Workshop. Abstract: I will review the atomic cluster expansion for constructing hybrid mechanistic / data-driven interatomic potentials and other coarse-grained models from ab initio models. The method can be interpreted as a polynomial regression scheme, but despite (or maybe because of) its simplicity it naturally leads to high performance, crystal clear interpretability and excellent generalization properties. I will explain the key idea and then show-case a few features that make it a general and flexible modelling tool, for linear and nonlinear, invariant or covariant, atomic or global, properties, as well as a few of the first emerging models based on ACE methodology. Finally, I will summarize our attempts to rigorously justify the atomic cluster expansion from first principles, for example explaining how an in principle complex many-body model can be decomposed into local and low-dimensional components in various different ways. Learn more online at: http://www.ipam.ucla.edu/programs/workshops/workshop-i-multiscale-approaches-in-quantum-mechanics/?tab=schedule