Phonopy

Phonopy (Backend-Agnostic)

Use this skill as a general phonon orchestration layer.

It treats force calculation as a pluggable backend step and focuses on phonopy data flow.

Scope

This skill should:

• generate displacement supercells from a user-provided structure
• define and validate force-collection requirements
• build force constants from collected forces
• run phonon analysis (band, DOS, thermal properties)
• summarize assumptions and remaining decisions

This skill should not:

• assume a single force engine
• fabricate force data
• submit cluster jobs directly

If execution/submission is required, hand off run steps to submission skills (for example dpdisp-submit) and backend-specific input skills.

Hard requirement

Phonon workflows require both:

• a valid initial structure (unit cell / primitive context)
• force data on displaced supercells (or precomputed force constants)

If either is missing, stop and ask for it.

Backend abstraction

Force provider may be one of:

• DFT backend (for example VASP or QE)
• ML force field backend (for example DeePMD/LAMMPS)

The role split should be:

• phonopy skill: displacement generation, dataset/force-constant assembly, phonon analysis
• backend skill: compute forces for each displaced supercell

Expected workflow

• Read and validate initial structure.
• Confirm phonon objective (band, dos, thermal, combinations).
• Choose supercell and displacement settings.
• Generate displaced supercells (phonopy -d style).
• Route displaced structures to selected backend for force evaluation.
• Collect forces and build FORCE_SETS or force constants.
• Run requested phonon analysis and export outputs.
• Report assumptions, convergence caveats, and next steps.

For concrete command patterns, see references/commands-and-workflow.md.

Parameters to collect

Must provide

• initial structure file (placeholder examples like structure.ext mean real files such

as POSCAR, .cif, or other backend-compatible structure formats)

• backend choice for force evaluation
• supercell setting (matrix or size)
• displacement amplitude (--amplitude policy)
• target phonon outputs (band, dos, thermal)

Usually should be explicit

• primitive matrix choice
• symmetry tolerance settings
• q-point mesh for DOS/thermal calculations
• band path definition source (if band requested)

Task-specific

For band:

• high-symmetry path definition
• number of points per segment

For dos/thermal:

• mesh density
• temperature range/step for thermal properties

Required behavior

• Validate structure periodicity and cell.
• Make backend boundary explicit before running force steps.
• Keep traceable mapping between each displacement and force file.
• Check force dataset completeness before force-constant build.
• Report non-analytic corrections / long-range settings status when relevant.
• Flag unresolved scientific choices instead of guessing silently.

Defaulting policy

Allowed only for low-risk defaults with explicit labels.

Reasonable defaults:

• finite-displacement workflow as baseline
• moderate displacement amplitude for first pass
• standard mesh/band resolution for exploratory analysis

Do not silently invent:

• backend force results
• production-level convergence settings
• band path conventions when crystal standard is unclear

Expected output

Provide:

• generated displacement task layout
• force-data assembly status (FORCE_SETS/force constants)
• requested phonon outputs (band/DOS/thermal files)
• explicit assumptions and unresolved decisions
• handoff guidance if backend execution/submission is pending

Common failure points

• missing or inconsistent force files for displacements
• supercell too small for stable phonon results
• inconsistent units/conventions across backend outputs
• imaginary modes caused by insufficient convergence or setup choices
• unclear band path convention for non-standard cells