Dear all,

Hope you all have a great day.

I tried CASTEP MEP calculation, but it always fails with the same error message.

"Cold fusion diagnosed - STOP. Energy and limit:     -1517247.537        -1000000.000"

The details are below:

System (bulk hopping path)

Material: Bulk ceria (CeO₂), cubic fluorite–type supercell, a = b = c = 10.9956 Å, α = β = γ = 90° (3D PBC, no vacuum).

Composition: 94 atoms total — Ce 32, O 62 (i.e., O-deficient vs. the 2×2×2 fluorite cell; two O vacancies present).

Event: Single O-atom hop in the bulk between adjacent anion sites (hopping model).

Moving atom: O (index 52, 1-based).

Initial fractional: (0.3969409, 0.6225088, 0.8774937)

Final fractional (shortest-image): (0.6069049, 0.6238314, 0.8761735)

Displacement vector (Å): (~2.3087, ~0.0145, ~−0.0145) — ~2.309 Å, nearly along x ([100]-like).

Endpoints: Identical lattice, identical species list/order; bulk configuration only (no surfaces).

I tried the number of images, spring constant, and even additional optimization of the bulk.

If there's any idea to solve this, please let me know.

Best regards,

Rakhoon Choi