4_epw/diamond.jl

#!/usr/bin/env julia
#=
EPW electron-phonon coupling workflow for diamond using ElectronPhonon.jl.
Generates frozen-displacement (FD) EPC braket files compatible with EPW.

Workflow (set flags at top):
  create  = true  → create symmetry-reduced displacement structures
  run     = true  → run QE SCF for all structures
  prepare = true  → read QE output, create JLD2 eigenvalue/phonon files
  calc_ep = true  → compute FD EPC brakets → displacements/epw/ (save_epw=true)

After calc_ep, run the standalone QE/EPW workflow (see run.sh):
  SCF → NSCF → ph.x → epw0 (Wannierize) → epw1 (DFPT ref) → parse_ml_data.py → epw2

Usage:
  cd example/diamond/4_epw
  julia diamond.jl
=#
using ElectronPhonon, PythonCall, ProgressMeter

# ============================================================
# Workflow flags — set interactively or via command-line ARGS:
#   julia diamond.jl create run prepare calc_ep
# ============================================================
create      = "create"  in ARGS || false
from_scratch = "scratch" in ARGS || false
run         = "run"     in ARGS || false
prepare     = "prepare" in ARGS || false
calc_ep     = "calc_ep" in ARGS || false

# ============================================================
# Paths
# ============================================================
SCRIPT_DIR   = @__DIR__
path_to_calc = SCRIPT_DIR * "/"

# Path to QE binary directory (must contain pw.x).
# Update to match your local QE installation.
path_to_qe = "/home/apolyukhin/Development/q-e_tmp/"

mpi_ranks = 8

# ============================================================
# Diamond FCC primitive cell (a = 3.567 Å)
# EPW uses only 4 valence bands; nosym/noinv for all 216 k-pts in save/
# ============================================================
a       = 3.567
sc_size = [1, 1, 1]
k_mesh  = [6, 6, 6]

pseudo_dir = SCRIPT_DIR * "/../pseudos/"

unitcell = Dict(
    :symbols          => pylist(["C", "C"]),
    :cell             => pylist([
        [0.0,  a/2, a/2],
        [a/2,  0.0, a/2],
        [a/2,  a/2, 0.0]
    ]),
    :scaled_positions => pylist([
        (0.0,  0.0,  0.0),
        (0.25, 0.25, 0.25)
    ]),
    :masses           => pylist([12.011, 12.011]),
)

# nosym/noinv: ensures all 216 k-pts are in scf.save/ for fake2nscf eigenvalue patching
scf_parameters = Dict(
    :format              => "espresso-in",
    :kpts                => pytuple((k_mesh[1], k_mesh[2], k_mesh[3])),
    :calculation         => "scf",
    :prefix              => "scf",
    :outdir              => "./tmp/",
    :pseudo_dir          => pseudo_dir,
    :ecutwfc             => 60,
    :conv_thr            => 1.0e-13,
    :pseudopotentials    => Dict("C" => "C.upf"),
    :diagonalization     => "david",
    :mixing_mode         => "plain",
    :mixing_beta         => 0.7,
    :crystal_coordinates => true,
    :verbosity           => "high",
    :tstress             => false,
    :ibrav               => 0,
    :tprnfor             => true,
    :nbnd                => 4,
    :electron_maxstep    => 1000,
    :nosym               => true,
    :noinv               => true,
)

# use_symm=true: symmetry-reduced displacements compatible with EPW
abs_disp = 1e-3  # Angstrom
use_symm = true

# Ensure pw.x is on PATH when Julia runs QE subprocesses
ENV["PATH"] = path_to_qe * "bin:" * get(ENV, "PATH", "")

model = create_model(
    path_to_calc   = path_to_calc,
    abs_disp       = abs_disp,
    path_to_qe     = path_to_qe,
    mpi_ranks      = mpi_ranks,
    sc_size        = sc_size,
    k_mesh         = k_mesh,
    unitcell       = unitcell,
    scf_parameters = scf_parameters,
    use_symm       = use_symm,
)

# When not creating, detect existing displacement dirs to set Ndispalce
if !create
    disp_dir = path_to_calc * "displacements/"
    if isdir(disp_dir)
        n = length(filter(d -> startswith(d, "group_"), readdir(disp_dir)))
        model.Ndispalce = n
        println("Detected $n displacement groups from displacements/")
    end
end

# ============================================================
# Step 1: Create displacement structures
# ============================================================
if create
    println("Creating symmetry-reduced displacement structures...")
    create_disp_calc!(model; from_scratch = from_scratch)
    println("Done. Created displacements/scf_0/ and symmetry-reduced group dirs.")
end

# ============================================================
# Step 2: Run QE SCF for all structures
# ============================================================
if run
    println("Running QE SCF for all displacement structures...")
    run_calculations(model)
    println("Done. QE calculations complete.")
end

# ============================================================
# Step 3: Prepare model
# ============================================================
if prepare
    println("Preparing model (reading QE output, creating JLD2 files)...")
    prepare_model(model)
    electrons = create_electrons(model)
    phonons   = create_phonons(model)
    println("Done. JLD2 eigenvalue and phonon files created.")
end

# ============================================================
# Step 4: Compute FD EPC brakets (save_epw=true → displacements/epw/)
# ============================================================
if calc_ep
    electrons = load_electrons(model)
    phonons   = load_phonons(model)

    ik_list = collect(1:prod(k_mesh .* sc_size))  # 1..216
    iq_list = [1]  # q=Gamma only

    mkpath(path_to_calc * "displacements/epw")
    progress = Progress(length(ik_list) * length(iq_list), dt=5.0)
    println("Computing FD EPC brakets for $(length(ik_list)) k-points (q=Gamma)...")

    for ik in ik_list
        for iq in iq_list
            electron_phonon(model, ik, iq, electrons, phonons; save_epw = true)
            next!(progress)
        end
    end
    println("Done. FD braket files written to displacements/epw/")
    println("Next: run the standalone QE/EPW workflow (see run.sh), then parse_ml_data.py")
end