3_epc/diamond.jl

#!/usr/bin/env julia
#=
DFT electron-phonon coupling calculation for diamond using ElectronPhonon.jl.

Workflow (set one flag to true at a time):
  create  = true  → create EPC displacement structures in displacements/
  run     = true  → run QE SCF + pw2bgw for all structures
  prepare = true  → read QE output, create JLD2 eigenvalue/phonon files
  calc_ep = true  → compute DFT EPC matrix elements → displacements/out_dft/

Usage:
  cd example/diamond/3_epc
  julia diamond.jl
=#
using ElectronPhonon, PythonCall, ProgressMeter

# ============================================================
# Workflow flags — set ONE to true at a time
# ============================================================
create      = false
from_scratch = false
run         = false
prepare     = false
calc_ep     = true

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

# Path to the QE binary directory (must contain pw.x and pw2bgw.x).
# Update this to match your local QE installation.
path_to_qe = "/home/apolyukhin/Development/q-e_tmp/"

mpi_ranks = 8  # from params.json execution.mpi_np

# ============================================================
# Diamond FCC primitive cell (a = 3.567 Å, matches scf.in)
# ============================================================
a        = 3.567
sc_size  = [1, 1, 1]
k_mesh   = [6, 6, 6]
natoms   = 2
Ndisplace = 6 * natoms  # 12: 2 atoms × 3 directions × 2 signs

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]),
)

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             => 8,
    :electron_maxstep => 1000,
    :nosym            => true,
    :noinv            => true,
)

abs_disp = 1e-3  # Angstrom

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,
    Ndispalce      = Ndisplace,
    unitcell       = unitcell,
    scf_parameters = scf_parameters,
    use_symm       = false,
)

# ============================================================
# Step 1: Create displacement structures
# ============================================================
if create
    println("Creating displacement structures in displacements/...")
    create_disp_calc!(model; from_scratch = from_scratch)
    println("Done. Created displacements/scf_0/ and displacements/group_1..$(Ndisplace)/")
end

# ============================================================
# Step 2: Run QE SCF + pw2bgw
# ============================================================
if run
    println("Running QE SCF + pw2bgw for all $(Ndisplace + 1) structures...")
    run_calculations(model)
    println("Done. QE calculations complete.")
    println("Next: run HPRO reconstruction via ml_epc.py (step 'hpro'), then set prepare=true")
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. Eigenvalue and phonon JLD2 files created.")
end

# ============================================================
# Step 4: Compute DFT EPC matrix elements
# ============================================================
if calc_ep
    electrons = load_electrons(model)
    phonons   = load_phonons(model)

    disp_dir = path_to_calc * "displacements/"
    out_dir  = disp_dir * "out/"
    out_dft  = disp_dir * "out_dft/"

    ik_list = collect(1:prod(k_mesh))
    iq_list = [1]

    progress = Progress(length(ik_list) * length(iq_list), dt=5.0)
    println("Calculating DFT EPC for $(length(ik_list)) k-points...")

    for ik in ik_list
        for iq in iq_list
            electron_phonon(model, ik, iq, electrons, phonons; phonons_dfpt=false)
            next!(progress)
        end
    end

    # Rename out/ → out_dft/ to preserve DFT reference
    if isdir(out_dft)
        rm(out_dft; recursive=true)
    end
    if isdir(out_dir)
        mv(out_dir, out_dft)
        println("Done. DFT EPC saved to: displacements/out_dft/ ($(length(readdir(out_dft))) files)")
    else
        println("WARNING: out/ not found after EPC calculation.")
    end
end