What is energy above hull (Ehull)?

Energy above hull (Ehull, in eV/atom) measures how far a material is from the thermodynamic convex hull — the set of most stable phases at each composition in a chemical system.

Interpretation

• Ehull = 0: The material is on the convex hull and is a thermodynamically stable phase
• Ehull < 0.025 eV/atom: Very close to stable; likely synthesizable or may exist as a metastable phase
• Ehull = 0.025 - 0.100 eV/atom: Moderately metastable; may be accessible under specific synthesis conditions
• Ehull > 0.100 eV/atom: Significantly unstable; unlikely to be synthesized in bulk equilibrium conditions

Why It Matters

Ehull is the single most important stability metric in computational materials science. Screening for Ehull < 0.05 eV/atom is a standard first filter when searching for synthesizable candidate materials.

How It Is Computed

The convex hull is constructed from formation energies of all known phases in a chemical system. Ehull is the energy difference between a material and the hull at its composition. The Materials Project computes this using the full database of known phases.