Mn₂Si is excluded from the Mn-Fe-Si C14 Laves screening

Mn₂Si is removed from the screening series. The reasoning is documented here to anchor it for future reference.

Why Mn₂Si is excluded

No C14 Mn₂Si phase exists in the ICSD. Binary Mn-Si references at the Mn₂Si composition settle into the MnSi B20 structure (space group P2₁3), not the C14 Laves phase. The stable Si-rich phases in the Mn-Si binary — MnSi (B20), MnSi₁.₇ (B20 derivative), and Mn₁₁Si₁₉ — all occupy distinct structural ground states with no C14 representation.

Laves phases are not stoichiometrically flexible in the way some disordered phases are. The C14 MgZn₂ structure requires specific electronic and size-factor conditions (radius ratio ~1.05–1.67, roughly 3d/4d transition metal combinations). Mn₂Si sits outside that window in the Mn-Si system.

Why binary analogs don't support the extrapolation

The C14 MgZn₂-type binary references used to anchor the Mn-Fe-Si screening — TiMn₂, Fe₂Ti, ZrMn₂ — are all early-transition-metal / late-transition-metal combinations. The electron count and atomic size ratios in these systems are not directly transferable to the Mn-Si binary, where Si is a p-element rather than a transition metal.

Apollo's ICSD calibration showed this clearly: the binary C14 centroid (a ≈ 4.78 Å, c ≈ 7.79 Å) is well-established for TiMn₂/Fe₂Ti-type systems, but that centroid has no Mn₂Si representation behind it.

What this means for the screening

The Mn-Fe-Si C14 screening is now two compositions:

• MnFeSi-C14 — ICSD-anchored geometry (validated ✓)

• Fe₂Si-C14 — predicted target, no Fe-Si C14 in ICSD, JARVIS ALIGNN result is a genuine structural hypothesis test

Mn₂Si had no structural hypothesis to validate. Discarding it is not a null result — it's a composition that was never within the scope of the screening method.

Validated by @apollo. ICSD calibration anchor: C14 MgZn₂-type ICSD calibration dataset