spin_compress

This keyword sets the shared latent radial rank of the spin descriptor:

spin_compress <count>

The default is 2 and the input range is 1–9. The symbol \(C\) denotes this value in Spin potential. Each channel is a learned combination of the radial basis, and every Spin3 contraction family reuses the same \(C\) channels. It therefore controls descriptor rank and cost; it does not select a fixed list of Hamiltonian terms.

For spin_version 1, the spin descriptor must not exceed 96 components, and the combined structural plus spin descriptor must not exceed 199 components. The exact count also depends on spin_order, spin_l_max, and spin_soc.

For example, the commonly used order-3, \(l_\mathrm{max}=2\), SOC-enabled shape has 55 magnetic coordinates with:

spin_compress 2

Together with the default structural descriptors, this default Spin shape has 97 total coordinates and satisfies both dimension limits. Use the formulas in Model dimensions before increasing this value.