How to analyse results¶

Checking whether the workflow succeeded¶

from aiida import orm

node = orm.load_node(<pk>)

if node.is_finished_ok:
    print("Workflow finished successfully")
elif node.is_excepted:
    print("Workflow raised an exception")
else:
    print(f"Exit status {node.exit_status}: {node.exit_message}")

Retrieving the converged supercell¶

# AiiDA StructureData node
supercell = node.outputs.Converged_supercell

# Export to various formats
print(supercell.get_formula())

py_struc = supercell.get_pymatgen_structure()
py_struc.to(filename="converged_supercell.cif")   # CIF
py_struc.to(filename="POSCAR")                     # POSCAR / VASP

ase_struc = supercell.get_ase()

Retrieving the supercell transformation matrix¶

sc_matrix_node = node.outputs.Converged_SCmatrix
sc_matrix = sc_matrix_node.get_array('sc_mat')   # 3×3 integer numpy array

print("Supercell matrix:")
print(sc_matrix)

The transformation matrix M satisfies:

A_supercell = M @ A_unitcell

where A are the rows of the lattice matrix (each row is a lattice vector).

Understanding the muon position¶

The muon is added to the supercell as the last atom, represented as a hydrogen (H) species. Its fractional coordinates are:

py_struc = supercell.get_pymatgen_structure()
muon_site = py_struc[-1]                   # last site
print(muon_site.species_string)            # 'H'
print(muon_site.frac_coords)               # fractional coordinates in the supercell

The muon is placed at the first Voronoi interstitial site of the unit cell, with a small +0.001 offset in each fractional coordinate to lift degeneracy.

Inspecting the calculation provenance¶

Use verdi to explore the full provenance graph:

verdi node show <pk>
verdi process status <pk>
verdi node graph generate <pk>   # generates a PDF provenance graph

From Python:

# List all sub-processes
for called in node.called_descendants:
    print(called.pk, called.process_label, called.exit_status)

Common failure modes¶

Exit code	Label	Typical cause	Suggested action
402	`ERROR_SUB_PROCESS_FAILED_SCF`	SCF did not converge	Increase `electron_maxstep`, lower `mixing_beta`, check pseudos
403	`ERROR_RELAXATION_FAILED`	Unit cell relaxation failed	Check structure geometry; try a different `relax_type`
702	`ERROR_NUM_CONVERGENCE_ITER_EXCEEDED`	Supercell never converged	Increase `max_iter_num`, lower `conv_thr`, check that the structure is reasonable
704	`ERROR_FITTING_FORCES_TO_EXPONENTIAL`	Force data does not decay exponentially	Check that the SCF forces are physical; inspect forces manually