Robocrystallographer descriptions may be present in the pre-training data of the CodeGen-350M-mono model since it was trained on code from GitHub. However, we note that the untrained model fails to mimic the function of the fine-tuned model; see the SI for details and a brief discussion later.) Robocrystallographer generates text descriptions programmatically and deterministically: an advantage of this approach is consistency and accuracy, but a downside is the very structured and narrow form of the descriptions, as the data do not necessarily follow the typical conventions a practitioner might use to describe a structure informally. In other words, high accuracy is traded for limited variation in the description. This text contains crystallographic heuristics and represents structural components of a crystal relative to each other rather than in an absolute manner. For example, it does not contain structural parameters but describes how crystal subunits such as tetrahedra and octahedra are positioned and lists bond lengths. Since this description can be lengthy, we split it by sentence and capped it with a cumulative length cutoff of 400 characters.