Figure 19.

Hierarchical descriptors and fitting at the example of a general-purpose GAP for phosphorus.¹⁶³ (a) Combination of 2-body and SOAP terms constitutes the short-range GAP model—both terms being fitted simultaneously, with appropriate scaling factors, similar to ref (122). In addition, a 1/r⁶ (or “R6”) term is used, with a much longer cutoff. (b) Illustration of how these terms are smoothly brought to zero in the region up to the cutoff. (c) V_R6 term for longer-range interactions. (d) Phosphorene exfoliation curve, showing the performance of the combined “GAP+R6” model (red) compared to a short-range GAP (gray dashed line), the DFT+MBD reference (black dashed line), and high-level quantum chemistry benchmark data (blue and green markers). Reprinted from ref (163), where more detail and references may be found. Original figure published under the CC-BY 4.0 license (https://creativecommons.org/licenses/by/4.0/).