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Units & Conventions

MACE and ASE use consistent internal units. All values displayed in the web interface use these units directly — no conversions are applied.

Unit system

Quantity Unit Notes
Energy eV (electron volts)
Forces eV/A (eV per Angstrom)
Distances / positions A (Angstroms)
Stress eV/A^3
Temperature K (Kelvin)
Time fs (femtoseconds) Internally converted via ase.units.fs
Pressure GPa (user-facing) 1 GPa = 10,000 bar; internally eV/A^3

Conversion at boundaries

Boundary Energy Forces Distance Time Temperature Pressure
User input - - A fs K GPa
ASE internal eV eV/A A ASE units K eV/A^3
MACE output eV eV/A A - - -
JSON result eV eV/A A seconds - -
Frontend display eV eV/A A seconds K GPa

Critical conversion

Pressure from user-facing GPa to ASE internal bar: pressure_GPa * 1e4 = pressure_bar

Common pitfalls

  1. Never mix units — MACE outputs eV/A, ASE uses eV/A internally, display is eV/A
  2. Reference energies vary — extended XYZ metadata keys can be REF_energy, ref_energy, energy, or dft_energy
  3. Benchmark catalog values are experimental — not DFT. Comparisons must note this
  4. MACE-MP-0 vs MACE-OFF energy ranges differ by an order of magnitude due to different reference conventions