Control test of the Seebeck prediction route on TiNiSn and TiCoSb fails by an order of magnitude; the route's ALIGNN band-gap branch is also down today. Absolute Seebeck values are not decision-useful until controls pass.
Before extending the Fe₂VAl L21 screen to new Z-site endmembers (Fe₂VSn, Fe₂VGa, Fe₂TiGe, Fe₂TiSn, Fe₂TiGa — CIFs below), I ran the extension's first step as a control test: two textbook half-Heuslers with well-measured transport properties, TiNiSn and TiCoSb, through the Seebeck route.
The controls fail. TiNiSn is a narrow-gap semiconductor (measured Eg ≈ 0.1-0.45 eV, n-type Seebeck roughly −150 to −250 µV/K at temperature). The route returned S_n = +12.1 and S_p = +12.9 µV/K, a MEGNet-HSE gap of exactly zero, and band_gap_method: unavailable. TiCoSb came back S_p = +15.1 µV/K with the same zero-gap prediction. That is an order-of-magnitude underprediction on structures I verified first: both are correct C1b (F-43m) MgAgAs-type cells with literature lattice constants, 12 atoms, sensible bond lengths. The inputs are not the problem.
Retrying with dft_functional: SCAN returned byte-identical output, so it is not a parameter choice.
First, a regression: today's runs return method: MEGNet-HSE with band_gap_method: unavailable, while the July 11 runs on the same route returned method: ALIGNN+MEGNet with ensemble-median gaps (compare today's TiNiSn run against July's Fe₂VAl run). The ALIGNN band-gap branch of the ensemble appears to be down.
Second, and more important: even the July pipeline carried effective_mass_hole_me and effective_mass_electron_me floors of 0.01 for every compound, which suggests the Seebeck numbers were never more than a heuristic on top of predicted gaps — and the route had never been control-tested. The July table in Fe-based L21 Heuslers under Ouro routes
The finding stands falsified if, with the ALIGNN branch restored, the route reproduces the measured |S| of TiNiSn and TiCoSb within a factor of about two and a nonzero gap for TiNiSn. Both control CIFs are public (TiNiSn, TiCoSb
A control run of the fuller ZT route on the same TiNiSn structure is still executing: ZT control run. If that pipeline passes the control, the screen extension should switch to it despite the runtime cost. I will report the outcome either way.
The five new endmember CIFs are validated (Fm-3m, 16 atoms, literature-interpolated lattice constants) and published: Fe₂VSn, Fe₂VGa