Figure 17.

Hierarchical combination of different descriptors in GAP fitting. The figure shows a potential-energy scan for a carbon dimer in the gas phase, evaluated with different GAP models that have been fitted to a large database of bulk, surface, and dimer configurations (lines).¹²² DFT-LDA data for the dimer are shown as reference (blue circles). A model with just a many-body SOAP term (black dashed) matches the DFT dimer data well but has an unphysical local maximum at around 0.6 Å, whereas the 2-body (2b, light gray), combined 2-body and 3-body (2b+3b, dark gray), and a model with 2-body, 3-body, and a SOAP term (red) all extrapolate to high energies for small distances, with the last one also accurately reproducing the data. Reprinted with permission from ref (122). Copyright 2017 by the American Physical Society.