A general method to obtain a representation of the structural
landscape
of nanoparticles in terms of a limited number of variables is proposed.
The method is applied to a large data set of parallel tempering molecular
dynamics simulations of gold clusters of 90 and 147 atoms, silver
clusters of 147 atoms, and copper clusters of 147 atoms, covering
a plethora of structures and temperatures. The method leverages convolutional
neural networks to learn the radial distribution functions of the
nanoclusters and distills a low-dimensional chart of the structural
landscape. This strategy is found to give rise to a physically meaningful
and differentiable mapping of the atom positions to a low-dimensional
manifold in which the main structural motifs are clearly discriminated
and meaningfully ordered. Furthermore, unsupervised clustering on
the low-dimensional data proved effective at further splitting the
motifs into structural subfamilies characterized by very fine and
physically relevant differences such as the presence of specific punctual
or planar defects or of atoms with particular coordination features.
Owing to these peculiarities, the chart also enabled tracking of the
complex structural evolution in a reactive trajectory. In addition
to visualization and analysis of complex structural landscapes, the
presented approach offers a general, low-dimensional set of differentiable
variables that has the potential to be used for exploration and enhanced
sampling purposes.