Connectivity optimized nested line graph networks for crystal structures

Graph neural networks (GNNs) have been applied to a large variety of applications in materials science and chemistry. Here, we systematically investigate the graph construction for crystalline (periodic) materials and investigate its impact on the GNN model performance. We propose the asymmetric unit cell as a representation to reduce the number of nodes needed to represent periodic graphs by exploiting all symmetries of the system. Without any loss in accuracy, this substantially reduces the computational cost and thus time needed to train large graph neural networks. For architecture exploration we extend the original Graph Network framework (GN) of Battaglia et al., introducing nested line graphs (Nested Line Graph Network, NLGN) to include more recent architectures. Thereby, with a systematically built GNN architecture based on NLGN blocks, we improve the state-of-the-art results across all tasks within the MatBench benchmark. Further analysis shows that optimized connectivity and deeper message functions are responsible for the improvement. Asymmetric unit cells and connectivity optimization can be generally applied to (crystal) graph networks, while the suggested nested NLGN framework can be used as a template to compare and build more GNN architectures.