Similarly, one can add higher-order equivariant features into the network. For example, the tensorial atomic property 5 P ixy incorporating 5 r ijxy and its corresponding PI and IP operations have also been implemented in PiNet2 (see the top part of Fig. colored in green). Here, 5 r ij is the 5-component irreducible representation of the outer product of the bond vector, which was used in practice for computational efficiency.