The second NN model is the MLRNet, which is a newly developed model and has been used for H 2 O-Ar system before. The COM distance R and normalized FIs form the input of the MLRNet. Unlike those of FI-NN, the FIs used for the MLRNet are R-independent, which are constructed from the atomic distance directly in a constant COM distance R fix = 4.0 Å. In practice, the outputs of the MLRNet also need a normalization procedure. Here, we simply take the 1-D MLR fitting results of dense grids to guess the value of those MLR parameters.