For the distance selector, we use the local outlier factor (LOF) method to determine whether the SOAP vector of the new configuration is an outlier compared to the SOAP vectors of the existing training data. LOF is based on the local density of each point, which is calculated by measuring the Euclidean distance between the target point and its k-nearest neighbours (Fig. ). The local reachability density of an object o, denoted as lrd k (o) is calculated as: