SLayerGen: a Crystal Generative Model for all Space and Layer Groups

TL;DR

SLayerGen is a novel generative model designed to create diperiodic crystal structures invariant to space and layer groups, advancing the modeling of 2D materials and surfaces.

Contribution

It introduces a new generative approach incorporating layer group symmetries, dataset assembly, and evaluation metrics for diperiodic materials.

Findings

SLayerGen outperforms bulk crystal models in diperiodic structure generation.

The model is competitive when trained on both bulk and diperiodic datasets.

Corrected diffusion loss for hexagonal non-orthogonal groups enhances accuracy.

Abstract

Crystal generative models have shown rapid progress for accelerating the discovery of bulk, periodic materials. However, many material systems such as 2D superconductors, thin film semiconductors, and catalytic surfaces are diperiodic, i.e., aperiodic along one of the lattice directions. These systems are invariant under the layer groups, which are known to influence materials properties yet not considered by existing models. In this paper, we propose SLayerGen, a generative model that produces crystals constrained to be invariant to any space or layer group. SLayerGen consists of coarse-to-fine discrete autoregressive lattice generation; transformer-based autoregressive sampling of Wyckoff positions, elements, and numbers of symmetrically unique atoms; and space or layer group equivariant diffusion of atomic coordinates. For the diffusion component, we corrected an inconsistency in the loss from prior work arising from hexagonal groups being non-orthogonal in fractional coordinates. To facilitate progress in generative modeling of diperiodic materials, we assembled and filtered datasets of monolayers and bilayers, propose relevant evaluation metrics, and developed novel representations for layer group symmetries. For de novo generation of diperiodic materials, SLayerGen achieves consistent performance gains over bulk crystal generative models and is competitive when training jointly on bulk and diperiodic materials.