Spin multiplicity

The spin multiplicity of the system is associated with the "spin_multiplicity" or "spin_multiplicity/<variant>" name (see Output variants), and must have the following metadata:

Metadata for spin_multiplicity

Metadata	Names	Description
keys	"_"	the keys must have a single dimension named "_", with a single entry set to 0. The spin multiplicity is always a metatensor.torch.TensorMap with a single block.
samples	["system"]	the samples must be named ["system"], since the spin multiplicity is a per-system quantity. "system" must range from 0 to the number of systems given as input to the model.
components		the spin multiplicity must not have any components
properties	"spin_multiplicity"	the spin multiplicity must have a single property dimension named "spin_multiplicity", with a single entry set to 0.

The values represent the spin multiplicity \(2S + 1\) of the system, where \(S\) is the total spin quantum number. The values are dimensionless and stored as floats (matching the model’s dtype), even though they always take positive integer values. The value must be at least 1.

Common examples:

• 1 for a singlet (\(S = 0\))

• 2 for a doublet (\(S = 1/2\), e.g. a radical with one unpaired electron)

• 3 for a triplet (\(S = 1\))