Strange phonon dispersion fcc structure

Hello,

I tried to calculate phonon band structure for fcc lattice. Independently on which parameters I use (k- and q-point grid, with/without shiftk, q-path, material), I get the same wrong behavior around K/U high-symmetry point.
For example, band structure in copper:
image

I got the same dispersion following different ways. For example, via phonon workflow:

import os
import sys
import abipy.abilab as abilab
from abipy import flowtk

def make_scf_input(structure, ngkpt, tsmear, pseudos, paral_kgb=1):

scf_inp = abilab.AbinitInput(structure, pseudos=pseudos)

scf_inp.set_vars(
    istwfk="*1",
    ecut=50.0,
    nband=16,
    occopt=3,
    tsmear=tsmear,
    nstep=500,
    paral_kgb=paral_kgb,
    autoparal=4,
    wfoptalg=14)

# Dataset 1 (GS run)
scf_inp.set_kmesh(ngkpt=ngkpt, shiftk=structure.calc_shiftk())
scf_inp.set_vars(tolvrs=1e-10)

return scf_inp

def build_flow(options):
if not options.workdir:
options.workdir = os.path.basename(sys.argv[0]).replace(“.py”, “”).replace(“run_”, “flow_”)

structure = abilab.Structure.from_abivars(
    acell=[6.8313599418]*3,
    rprim=[
        [0.0, 0.5, 0.5],
        [0.5, 0.0, 0.5],
        [0.5, 0.5, 0.0]
    ],
    typat=1,
    xred=[0, 0, 0],
    ntypat=1,
    znucl=29)

pseudos = pseudos = "/gpfs/home3/fedorak/pseudos/Cu.psp8"

flow = flowtk.Flow(workdir=options.workdir)

scf_work = flowtk.Work()
ngkpt_list = [[16]*3]
tsmear_list = [1e-3]
for ngkpt in ngkpt_list:
    for tsmear in tsmear_list:
        scf_input = make_scf_input(structure, ngkpt, tsmear, pseudos)
        scf_work.register_scf_task(scf_input)
flow.register_work(scf_work)

for scf_task in scf_work:
    ph_work = flowtk.PhononWork.from_scf_task(scf_task, qpoints=[4]*3, is_ngqpt=True)
    flow.register_work(ph_work)

return flow.allocate(use_smartio=True)

@flowtk.flow_main
def main(options):
return build_flow(options)

if name == “main”:
sys.exit(main())

With the q-path provided in anaddb file:

ifcflag 1 ! Interatomic force constant flag
brav 2 ! Bravais Lattice : 1-S.C., 2-F.C., 3-B.C., 4-Hex.)
ngqpt 4 4 4 ! Monkhorst-Pack indices
nqshft 1 ! number of q-points in repeated basic q-cell
q1shft 3*0.0
nqpath 7
qpath 0.0000000 0.0000000 0.0000000 !\Gamma
0.5000000 0.0000000 0.5000000 !X
0.6250000 0.2500000 0.6250000 !U
0.0000000 0.0000000 0.0000000 !\Gamma
0.5000000 0.5000000 0.5000000 !L
0.5000000 0.2500000 0.7500000 !W
0.5000000 0.0000000 0.5000000 !X
ddb_filepath = “/abspath_to_workdir/outdata/out_DDB”
output_file = “anaddb.abo”

Hope someone can provide insights what I am doing wrong.

Dear Radioteddy,
The phonon band structure that you obtain is correct - given the q point path that you give to ABINIT…
qpath 0.0000000 0.0000000 0.0000000 ! Γ
0.5000000 0.0000000 0.5000000 !X
0.6250000 0.2500000 0.6250000 !U
0.0000000 0.0000000 0.0000000 ! Γ
0.5000000 0.5000000 0.5000000 !L
0.5000000 0.2500000 0.7500000 !W
0.5000000 0.0000000 0.5000000 !X
For example, if you compare it with the phonon band structure in Lan et al, Computational Materials Science, 149, 397 (2018), Fig. 4, the behaviour is the same for the Gamma-X-U, Gamma-L-W-X lines . For the U-Gamma line, this publication does not show it . If you want to obtain the K-Gamma line, you should define
0.375 0.375 0.75 !K
0.0 0.0 0.0 !Gamma
following the suggestion in Ground-State - abinit (and supposing that you are using the same rprim). Best wishes X.