The extracted SOAP spectra ( 2 × 10 6 for each of the 10 frames) of the Au atoms have been then classified based on a general AE dictionary of Au Np SOAP atomic environments, that we recently developed. In particular this comprehensive AE dictionary includes 47 SOAP spectra of all the AEs present in ideal Au NPs (at 0 K) of various sizes and morphologies at 0 K (Figure ). This provides us with an essential tool for monitoring the AEs that are present in the real NP under experimental conditions and to classify them based on their similarity to the AEs contained in the dictionary. Figure shows all the AEs present in adjacency (similar in term of SOAP spectrum). The dotted inner circle indicates that truncating the dendrogram, we consider only SOAP distance larger than 0.8 as relevant (an excessive resolution increases the noise and would emphasize irrelevant differences). This choice simplifies the dictionary from 47 to 11 without sacrificing significant variations (Figure ). In the adopted color scheme of the dendrogram of Figure , the colors belonging to the purple palette refer to native AEs typical of ideal truncated octahedral NPs, while all the other colors identify AEs that are more similar to AEs proper of other ideal NPs' morphologies (e.g. icosahedral, decahedral, etc.) Leveraging such "coarse-grained" dictionary, we colored the atoms in the ten experimentally reconstructed NP structures based on the similarity of their SOAP atomic environments to those within our SOAP dictionary (Figure ). This first analysis reveals the dynamic nature of the atomic environments within the NPs in experimental conditions over the 6-second data acquisition, during which the atoms of this octahedral Au NP move, and non-native AEs (colored in yellow, green, and red) emerge on the NP surface. Far from being static, these NP structures show remarkable variability driven by thermal effects.