Custom sets

atomref is not limited to the packaged tables. You can build a small user-defined element-indexed scalar dataset and use it as a base dataset or as a support dataset inside a transfer-backed policy.

The simplest entry point is ElementScalarSet.from_mapping(...).

from atomref import DatasetRef, ElementScalarSet, RadiiPolicy

custom = ElementScalarSet.from_mapping(
    ref=DatasetRef("covalent_radius", "my_cov"),
    values={"C": 0.75, "H": 0.31},
    name="My custom covalent radii",
    units="angstrom",
)

policy = RadiiPolicy(kind="covalent", base_set=custom)

This is useful when you want to:

• test an alternative reference table,
• pin a small project-specific dataset without creating a full package fork,
• combine a user dataset with built-in support data through substitution or linear transfer.

In the current implementation custom sets are element-domain scalar datasets, which keeps the data model small and stable. Later versions may add more specialized domains, but custom element-wise sets are already enough for many geometry workflows.