| { |
| "description": "Given the INCAR, POSCAR summary, and OUTCAR excerpt below, diagnose why structural relaxation diverges.", |
| "diagnosis_hint": "Two compounding issues: (1) POTIM=1.0 is far too large - the default 0.5 or even 0.1-0.3 would be safer; (2) starting from the wrong phase (cubic instead of orthorhombic) means initial forces are huge. Fix: reduce POTIM to 0.1-0.2, or better yet, start from the orthorhombic Pnma structure. For unknown ground-state structures, use a conservative POTIM with IBRION=1 (RMM-DIIS) which handles large steps better than conjugate gradient.", |
| "incar": { |
| "EDIFF": 1e-06, |
| "EDIFFG": -0.02, |
| "ENCUT": 450, |
| "IBRION": 2, |
| "ISIF": 3, |
| "ISMEAR": 0, |
| "ISPIN": 1, |
| "NSW": 300, |
| "POTIM": 1.0, |
| "PREC": "Accurate", |
| "SIGMA": 0.05, |
| "SYSTEM": "Perovskite_CsPbI3_cubic", |
| "_comment": "BUG: POTIM=1.0 is too large for this system. Combined with an initial structure that has the cubic phase (high-T) instead of the actual ground-state orthorhombic phase, the forces are large and POTIM=1.0 causes atoms to overshoot drastically. Each ionic step the structure bounces back and forth, never settling." |
| }, |
| "key_observation": "Energy increases from step 1 to step 4, forces explode from 2.3 to 48 eV/A, volume swings wildly. By step 5, VASP encounters a fatal bracketing error. The ionic step is too aggressive.", |
| "outcar_excerpt_ionic_steps": [ |
| "--- step 1: E= -19.23456 max_force= 2.341 volume= 248.9", |
| "--- step 2: E= -17.89123 max_force= 5.672 volume= 275.3", |
| "--- step 3: E= -12.34567 max_force= 12.891 volume= 312.1", |
| "--- step 4: E= +8.45231 max_force= 48.234 volume= 189.2", |
| "--- step 5: ZBRENT: fatal internal error", |
| " please rerun with smaller POTIM, or copy CONTCAR to POSCAR and continue" |
| ], |
| "poscar_summary": { |
| "counts": [ |
| 1, |
| 1, |
| 3 |
| ], |
| "lattice_a": 6.289, |
| "note": "Cubic CsPbI3 is the high-temperature phase; ground state is orthorhombic Pnma. Starting from cubic with ISIF=3 requires large atomic displacements and cell shape changes.", |
| "species": [ |
| "Cs", |
| "Pb", |
| "I" |
| ], |
| "system": "CsPbI3 cubic Pm-3m (high-T phase, NOT ground state)", |
| "total_atoms": 5 |
| }, |
| "root_cause": "potim_too_large_and_bad_initial_structure", |
| "task": "relax_divergence_diagnosis" |
| } |
|
|
