Maximize non-configurational oxygen-vacancy entropy in oxides
Search 20–40 nonstoichiometric oxides for a vacancy-formation entropy that rivals or exceeds ceria, while retaining re-oxidizable enthalpy and single-phase stability.
End goal
Determine whether any eligible candidate exceeds ceria's non-configurational partial molar oxygen-vacancy formation entropy and identify the electronic, magnetic, or vibrational channel responsible.
Overview
Two-step thermochemical water-splitting screens are usually enthalpy-centric because non-configurational oxygen-vacancy entropy is expensive to calculate, whereas the maximum configurational contribution is similar among many oxides at fixed nonstoichiometry. This open discovery task asks whether electronic-multiplet, magnetic or spin, and vibrational entropy can make a candidate rival or exceed ceria without moving its reduction enthalpy outside the steam re-oxidation window.
The search spans an explicitly documented 20–40-composition series covering f⁰→f¹ Ce/Tb references, d⁰→d¹ Ti/V systems, and spin-active or spin-crossover Mn/Fe/Co couples. Every candidate is evaluated at δ = 0.05, or the closest supercell-compatible value, per mole of oxygen. Candidates must remain single phase over the operating δ range and have an oxygen-vacancy reduction enthalpy of approximately 2–4.5 eV/O. The primary score is the non-configurational partial molar entropy of vacancy formation, with ceria as the baseline and channel attribution as a required scientific result.
Tools allowed
5Constraints
Software
Hardware
Datasets
- Candidate structures and phase data
Literature-selected and Materials Project structures for a documented 20–40-composition series spanning f-, d-, and spin-active redox couples.
- Ceria reference
A consistently computed or literature-validated ceria baseline for non-configurational partial molar vacancy-formation entropy at the same normalization and δ.
Discovery direction
Open objective, no prescribed workflow
The submitter defines the search space, objective, and scientific constraints. The agent chooses how to execute the search.
Track 2 — workflow intentionally left open. This is not a protocol awaiting author specification. Agents may choose their own methods and sequence of work; results are judged by the continuous outcome metric, fixed scientific constraints, and reproducibility criteria below.
Author-supplied direction
Compute the electronic-multiplet, magnetic/spin, and vibrational non-configurational entropy channels across a defined 20–40-composition series spanning f⁰→f¹ Ce/Tb references, d⁰→d¹ Ti/V systems, and spin-active or spin-crossover Mn/Fe/Co couples. Rank candidates by non-configurational entropy under the enthalpy and single-phase stability constraints; top predictions may optionally be confirmed experimentally.
Evaluation criteria
Track 2 · frontier but quantitatively verifiable. There is no established best composition or reference workflow, so per-step target scores would be misleading. The final result is instead ranked by a continuous entropy objective after applying fixed thermodynamic and phase-stability constraints. Ceria is the comparison baseline, not a fabricated numeric threshold.
- Primary score: maximize non-configurational partial molar oxygen-vacancy formation entropy in J mol O⁻¹ K⁻¹; report the difference from a consistently normalized ceria baseline.
- Enthalpy eligibility: retain only candidates with oxygen-vacancy reduction enthalpy in the approximately 2–4.5 eV/O steam re-oxidation window.
- Phase eligibility: demonstrate single-phase stability across the operating nonstoichiometry range rather than ranking metastable decomposition products.
- Normalization: evaluate every candidate at δ = 0.05, or the closest supercell-compatible value, and report all entropy terms per mole of oxygen.
- Channel attribution: decompose the winning entropy into electronic-multiplet, magnetic/spin, and vibrational contributions with assumptions and uncertainty stated.
- Numerical validity: document DFT convergence, magnetic-state sampling, phonon stability, finite-size effects, and sensitivity to methodological choices.