Imported from QuantumBFS/quantum.harness (skills/using-quantum-espresso/SKILL.md). Install upstream with npx skills add QuantumBFS/quantum.harness --skill using-quantum-espresso. Copyright stays with the author.

Using Quantum ESPRESSO

DFPT / electron-phonon coupling route

Software-stack skill for using Quantum ESPRESSO native DFPT-EPC to study electron-phonon superconductivity. It owns the package-level run mechanics: build SCF and PHonon inputs, keep IFC and EPC branches separate, monitor long ph.x jobs, diagnose fragile PHonon failures, and turn alpha2F(omega) into a qualified superconducting Tc estimate.

Method understanding, method-vs-method routing, and knob JUDGMENT live in method-dfpt; result interpretation lives in physics-electron-phonon-coupling.

Stack contract: skills/using-quantum-espresso/stack.toml. The reusable source templates live in skills/using-quantum-espresso/references/dfpt/:

prepare-qe-todo.md
input-sources.md
scf.in
ph_ifc.in
q2r.in
matdyn_disp.in
ph_dvscf_epc.in
elph_densek_alpha2f.in
run_epc_sbatch.template.sh

Do not embed pseudopotential files in this skill. references/dfpt/input-sources.md points to QE/SSSP download locations and records what the PdH-style templates assume.

Version assumptions

Skill/template revision: 2026-06-30.
Target route: Quantum ESPRESSO native PHonon EPC with lambda_tetra, as used by common QE 7.x PHonon builds and PHonon/examples/tetra_example/.
The exact QE build is not bundled with this skill. Before each run, record the installed QE version, executable paths, module or build prefix, and whether alpha2f.x is serial-only for that build.
Re-check input keywords against the installed QE documentation when using older QE 6.x builds, patched site builds, or future QE releases.

The workflow spine

The ordered workflow-spine overview block is method-layer UNDERSTANDING and lives in method-dfpt. -> method-dfpt "The workflow spine".

Use one directory per parameter point:

runs/<material-or-lattice>_q<N>_k<M>/
  pseudo/
  scf.in
  ph_ifc.in
  q2r.in
  matdyn_disp.in
  ph_dvscf_epc.in
  elph_densek_alpha2f.in
  run_epc.sbatch
  run_steps.tsv

Case names should be readable in a result table: include the structure or lattice tag, EPC q grid, and dense electron k grid.

Phase 1 - Prepare inputs (input keywords and templates)

Start from skills/using-quantum-espresso/references/dfpt/ and adapt values to the project.

SCF

Use scf.in as the pattern:

exact relaxed cell and atomic positions;
prefix, outdir, and pseudo_dir that match every PHonon input;
occupations = 'tetrahedra_opt' for the lambda_tetra route;
a dense explicit K_POINTS automatic grid;
project-validated ecutwfc, ecutrho, conv_thr, and mixing settings.

IFC branch

Use ph_ifc.in -> q2r.in -> matdyn_disp.in for ordinary force constants and phonon dispersion:

unshifted ldisp = .true. q grid;
q2r.x and matdyn.x only on this IFC branch;
asr / zasr selected according to the material and project convention.

EPC branch

Use ph_dvscf_epc.in for shifted-q dVscf generation:

ldisp = .true.;
lshift_q = .true.;
fildyn, fildvscf, and fildrho set explicitly;
recover = .true. allowed for restartable dVscf generation.

Then use elph_densek_alpha2f.in for dense-k lambda_tetra:

trans = .false.;
electron_phonon = 'lambda_tetra';
nk1, nk2, nk3 set to the dense electron k grid;
no recover = .true. in this dense-k lambda input;
&INPUTa2F nfreq = ... / present so the same file can feed alpha2f.x.

Run alpha2f.x serially unless the exact QE build has been verified to support parallel execution for that executable.

Phase 2 - Submit safely

Use references/dfpt/run_epc_sbatch.template.sh as a starting point for cluster jobs. Adapt the SBATCH header, modules, QE_ROOT, MPI launcher, NPOOL, and resource request to the target system.

Parallel settings

Treat the Slurm allocation, MPI rank count, QE pool count, and thread variables as one contract. Do not tune them independently.

Use a CPU-only pure-MPI default unless a project has validated hybrid MPI/OpenMP.
Set math-library threads to one for this default: OMP_NUM_THREADS=1, MKL_NUM_THREADS=1, OPENBLAS_NUM_THREADS=1.
Match the launch command to the allocation. A portable pure-MPI layout is:
```
#SBATCH --nodes=1
#SBATCH --ntasks-per-node=64
#SBATCH --cpus-per-task=1
NP="${SLURM_NTASKS}"
```
then run mpirun -np "$NP" ....
Some clusters prefer one Slurm task with many CPUs and a launcher that expands inside the allocated cpuset:
```
#SBATCH --nodes=1
#SBATCH --ntasks-per-node=1
#SBATCH --cpus-per-task=64
NP="${SLURM_CPUS_PER_TASK}"
```
Use this only after verifying that the site MPI launcher really starts NP MPI ranks inside the allocation.
Pass -npool "$NPOOL" to pw.x and the MPI ph.x steps. Choose NPOOL so it divides the MPI rank count and is sensible for the k-point count. Start conservative (1, 2, 4, or 8) and verify QE reports the expected pools.
Keep q2r.x, matdyn.x, and alpha2f.x serial unless the exact executable has been tested in parallel.
Print NP, NPOOL, thread variables, QE_ROOT, and the node list at job start. After the first run, check scf.out or ph*.out for the reported processor count and pool count before trusting timing or failures.

Before submission, check:

bash -n run_epc.sbatch
rg -n "occupations|K_POINTS|electron_phonon|trans|recover|nk1|nfreq" *.in
rg -n "recover *= *.true." elph_densek_alpha2f.in && echo "remove recover"

Then verify by inspection:

UPF names in ATOMIC_SPECIES exist under pseudo/.
All QE inputs use the same prefix and outdir.
Dense-k lambda_tetra input has trans = .false. and no recover.
A full-rerun wrapper archives old outputs before starting.
If IFC and EPC branches share one outdir, the wrapper archives tmp/_ph0 after matdyn.x and before ph_dvscf_epc.
The Slurm request, NP, NPOOL, and thread variables match the intended parallel layout.
The dense k grid stays below the QE build's k-point array limit. A set_kplusq: too many k points failure means reduce nk or rebuild QE with a larger npk.

Phase 3 - Monitor and diagnose

For live jobs, combine scheduler state with case-local evidence:

tail -n 20 run_steps.tsv 2>/dev/null
stat -c "%y %s %n" *.out 2>/dev/null
grep -E "Calculation of q|Representation #|JOB DONE|Error in routine|lambda|omega" -n *.out 2>/dev/null | tail -n 80
find . -maxdepth 1 \( -name "CRASH" -o -name "*.err" \) -type f -size +0 -print

Treat ph_ifc and ph_dvscf_epc as long-running stages. A job is slow/active, not stuck, when q-point or representation lines continue advancing and there is no non-empty .err, CRASH, or Error in routine.

Failure map

Symptom	Likely cause	Response
`opt_tetra_init (2): cannot remap grid on k-point list`	EPC branch is reading stale PH scratch, or the SCF k list is incompatible with the tetrahedron remap	First inspect `Reading xml data from directory` in `ph_ifc.out` and `ph_dvscf_epc.out`. If EPC reads `tmp/_ph0/<prefix>.save/`, archive `_ph0` and rerun from the EPC branch before changing grids.
`read_control_ph (1): wrong trans`	Dense-k `elph` step recovered a previous `ph.x` control file with a different `trans` mode	Remove `recover = .true.` from `elph_densek_alpha2f.in`; archive only old dense-k outputs and rerun the post-dVscf branch.
`read_lam: Imaginary frequency` in `alpha2f.x`	Shifted EPC q grid contains imaginary modes	Do not force a physical `Tc`. Inspect structural stability, q-grid dependence, and phonon branches first.
Shifted q grid cannot be used by `q2r.x`	EPC shifted q grid is being reused as an IFC interpolation grid	Keep unshifted IFC/dispersion and shifted EPC grids as separate branches.
`set_kplusq: too many k points`	Dense electron k grid exceeds the QE build's static k-point array	Reduce `nk` or rebuild QE with a larger `npk`; record the limit in the result note.

Phase 4 - Interpret results (data collection and Tc value)

After alpha2f.x succeeds, collect:

lambda from QE's direct omega_q/lambda_q summary;
omega_log / omega_ln, with units;
the alpha2F(omega) data file;
an independent alpha2F integration check when the data file is present;
Tc for at least mu* = 0.10, 0.13, 0.15;
IFC branch and shifted EPC q-grid imaginary-frequency status.

The McMillan/Allen-Dynes interpretation form and units rule live in physics-electron-phonon-coupling "Interpretation rules"; the convergence-comparison logic lives in method-dfpt "Convergence judgment".

Write a short result note beside the run tree with the case name, QE version, input grids, resources, step statuses, failure/success evidence, lambda, omega_log, Tc(mu*), imaginary-frequency status, and remaining convergence caveats.

Common mistakes (package mechanics)

Mistake	Instead
Reusing `tmp/_ph0` from the IFC branch for shifted-q EPC	Archive or separate PH scratch before `ph_dvscf_epc`.
Running `q2r.x` on the shifted EPC q grid	Use an unshifted IFC branch for `q2r.x` / `matdyn.x`.
Leaving `recover = .true.` in the dense-k `lambda_tetra` input	Keep `recover` only in compatible restartable PHonon branches.
Reporting `Tc` after `alpha2f.x` reports imaginary frequencies	Report the instability; do not treat that `Tc` as physical.
Calling a q4/k21 canary a converged result	Add q-grid and dense-k checks before presenting a final number.
Trusting `RUNNING` or quiet stdout as proof of health	Inspect `run_steps.tsv`, output timestamps, q progress, and error files.
Requesting one Slurm shape but launching a different number of MPI ranks	Make Slurm tasks, `NP`, `NPOOL`, and thread variables agree, then verify QE's reported processor and pool counts.

Integrations

Source templates: skills/using-quantum-espresso/references/dfpt/.
Stack contract: skills/using-quantum-espresso/stack.toml.
Run preparation checklist: skills/using-quantum-espresso/references/dfpt/prepare-qe-todo.md.
Input provenance and download locations: skills/using-quantum-espresso/references/dfpt/input-sources.md.
Cluster wrapper template: skills/using-quantum-espresso/references/dfpt/run_epc_sbatch.template.sh.
QE upstream reference: the installed QE documentation and PHonon/examples/tetra_example/ in a QE source tree.

QMCPACK orbital-generation route

Software layer (QE / pw2qmcpack side) of the QE -> QMCPACK Slater-Jastrow VMC/DMC workflow for periodic solids. Method understanding/routing lives in method-dmc; the QMCPACK side lives in using-qmcpack.

Source templates (QE side)

The reusable QE source templates are references/qmcpack-orbitals/qe_scf.in, references/qmcpack-orbitals/qe_nscf.in, and references/qmcpack-orbitals/pw2qmcpack.in (byte-exact copies). Stack contract and QMCPACK-side templates live in using-qmcpack.

Run-directory layout (QE side)

QE entries of the shared run directory, moved verbatim from using-qmcpack Run-directory layout (the QMCPACK entries and the enclosing runs/<system>_k<NxNyNz>/ block stay there):

  qe_tmp/
  qe_scf.in
  qe_nscf.in
  pw2qmcpack.in

Version assumptions (QE side)

Moved verbatim from using-qmcpack Version assumptions. -> the QMCPACK-side route (a QMCPACK 4.3.x complex-valued ESHDF/einspline solid workflow) and build-recording bullets in using-qmcpack.

Target route (QE portion): QE 7.5-style pw.x plus matching HDF5-enabled pw2qmcpack.x

Orbital handoff: pw2qmcpack.x writes <prefix>.pwscf.h5 under the QE outdir; QMCPACK XML href values point to that exact file.

Preflight (QE side)

Most of Phase 0 stays in using-qmcpack. -> the QMCPACK-side items there: "2. Structure" (relaxed structure, atom count, species labels, cell units, pressure/lattice provenance, size-matching) and "3. Pseudopotential pair" (matched norm-conserving QE UPF + QMCPACK XML; stop on ultrasoft UPF) in using-qmcpack Phase 0 - Preflight

QE-side Phase 0 items, moved verbatim from using-qmcpack:

Binaries: Verify pw.x, pw2qmcpack.x, and
Run directory state: Inspect old qe_tmp/, .save/, .pwscf.h5,

Generate QE orbitals

Start from references/qmcpack-orbitals/qe_scf.in, references/qmcpack-orbitals/qe_nscf.in, and references/qmcpack-orbitals/pw2qmcpack.in.

SCF

Use the target structure, the matched QE UPF, and project-validated cutoffs.
Run with enough k-points to converge the charge density.
Keep prefix, outdir, and pseudopotential names consistent with NSCF and pw2qmcpack.in.
Use the QE build that belongs with pw2qmcpack.x.

NSCF

Run at the exact full twist grid required by the QMC supercell.
Set nosym = .true. and noinv = .true. so QE writes every twist, not a symmetry-reduced subset.
Keep K_POINTS automatic synchronized with the intended twist count.
Do not change the structure, pseudopotential, or prefix between SCF and NSCF.

Conversion

Run pw2qmcpack.x after the NSCF completes.
Expect the ESHDF file under the QE outdir, often qe_tmp/<prefix>.pwscf.h5.
Keep the QMCPACK XML href pointed at that actual path, not a guessed file in the run-directory root.
Use a serial converter launch (PW2QMCPACK_NP=1) unless this exact converter build has been proven safe with MPI.

-> QMCPACK XML href keyword/value and ESHDF consumption in using-qmcpack

Submit safely (QE and converter parallelism)

"Treat QE parallelism and QMCPACK twist parallelism as different problems." (framing kept whole in using-qmcpack Submit safely) -> QMCPACK twist parallelism and the submission/inspection checklists in using-qmcpack

QE

Use QE_NP MPI ranks for pw.x.
Pass a project-validated -npool for SCF/NSCF when useful.
Verify QE reports the expected rank and pool counts in qe_scf.out and qe_nscf.out.

Converter

Default PW2QMCPACK_NP=1.
If the converter needs a special HDF5 library path, apply it only to the converter command rather than polluting the global QMCPACK runtime.

Consistency checks (QE side)

Moved verbatim from using-qmcpack Submit safely (the bash -n step, the QMCPACK *.xml grep, the pseudo//qmc_pseudo/ test, and the QMCPACK-side inspection bullets stay there):

rg -n "prefix|outdir|K_POINTS|nosym|noinv" qe_*.in pw2qmcpack.in

UPF names in QE ATOMIC_SPECIES exist under pseudo/.
SCF, NSCF, and pw2qmcpack.in use the same prefix and outdir.
The NSCF grid matches the intended twist count and has nosym plus noinv.
XML href points to the expected ESHDF under QE outdir.

Cluster wrapper template (QE stage)

The QE SCF/NSCF/pw2qmcpack execution stage is the launcher references/qmcpack-orbitals/run_qe_orbitals.template.sh (byte-exact copy): QE SCF, QE NSCF, pw2qmcpack invocation, ESHDF check, and the QE_BIN / PW2QMCPACK / QE_NP / QE_NPOOL / PW2QMCPACK_NP env handling. -> the QMCPACK-stage launcher using-qmcpack/references/run_qmcpack_dmc.template.sh in using-qmcpack.

Monitor and diagnose (QE side)

QE-stage output evidence, moved verbatim from using-qmcpack Monitor (the QMCPACK qmcpack_*.out / *.scalar.dat lines and the generic stat/grep -E *.out lines stay there):

grep -n "JOB DONE." qe_scf.out qe_nscf.out pw2qmcpack.out
test -s qe_tmp/*.pwscf.h5

The QE filenames of the live-job tail (moved from the tail -n 40 ... qmcpack_*.out line in using-qmcpack):

qe_scf.out qe_nscf.out pw2qmcpack.out

Failure map (QE side)

Orbital-stage rows, moved verbatim from the using-qmcpack failure map (the QMCPACK-side rows stay there):

Symptom	Likely cause	Response
QMCPACK cannot find `.pwscf.h5`	XML assumes the ESHDF is in the run root	Point `href` at the file under the QE `outdir`, e.g. `qe_tmp/<prefix>.pwscf.h5`.
NSCF or converted twist count is too small	QE symmetry reduced the k grid	Set `nosym=.true.` and `noinv=.true.` in NSCF and regenerate orbitals.
`pw2qmcpack.x` runs but no useful HDF5 appears	Wrong QE build, wrong prefix/outdir, or converter launched with a bad library/MPI setup	Use the QE build paired with `pw2qmcpack.x`; verify `prefix`, `outdir`, and converter library path.

Stack contract (QE stanzas)

The stack contract stack.toml (id = "quantum-espresso", language = "fortran") covers the QE/converter binaries: [install.site] command command -v pw.x && command -v pw2qmcpack.x, [smoke.cpu_mpi] command pw.x -h >/dev/null && pw2qmcpack.x -h >/dev/null, and [docs] qe = "https://www.quantum-espresso.org/Doc/". -> the QMCPACK stack contract in using-qmcpack/stack.toml.

Common mistakes (QE side)

Mistake	Instead
Using a QE ultrasoft pseudopotential for production QMC orbitals	Use a norm-conserving QE UPF and matching QMCPACK XML pair.
Choosing QE k-points before the QMC twist plan	Choose the QMC cell and twist grid first, then generate NSCF twists.

-> remaining (QMCPACK-side) common mistakes in using-qmcpack

Input provenance (QE side)

The QE-side input-provenance lines and run-preparation rows now live here: references/qmcpack-orbitals/input-sources.md (QE documentation, version, QE-UPF source lines, Units, ESHDF Location) and references/qmcpack-orbitals/prepare-qe-todo.md (section "## 4. QE Orbital Inputs", the QE rows of "## 1. Version And Build Record", "## 3. Pseudopotential Pair", "## 2. Structure Materials", and "## 6. Run Controls"). -> the matched-pair prose and the QMCPACK-side rows in using-qmcpack/references/input-sources.md and using-qmcpack/references/prepare-qmcpack-todo.md

using-quantum-espresso

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