Non-physical solution of the polaron calculation of 2D blue-P

[jack]

Dear,
I am attempting to calculate the hole polaron in two-dimensional blue phosphorus (blue P). However, during the EPW calculation, an error message appears: "Non-physical solution, check initial guess and convergence."

The monolayer blue P structure contains two equivalent P atoms. The valence band comprises 5 bands without spin polarization.
First, I performed Wannierization using the projection: proj(1) = 'f=0.3333333330,0.6666666670,0.4705074384:p', with nbndsub = 3 and bands_skipped = 'exclude_bands = 1-2, 6-20'. The fitted bands agree well with the DFT results. It should be noted that wannier_plot_supercell was set to 6 6 2, while the coarse q-point and k-point grids were 6 6 1. If wannier_plot_supercell is set to 6 6 1 or 6*n 6*n 1, the Wannierization fails with the error: "Wrong range in plotting WF cube".

Next, I proceeded to calculate the hole polaron. Despite using the parameters listed below, EPW reported a non-physical solution. After reducing niter_plrn to 12, the calculation ran without error and yielded a formation energy with an error of approximately 0.05 eV. However, the resulting polaron wavefunction appears anomalous: it is localized around 14 Å along the Z-axis, whereas the atoms are positioned near 9 Å. This indicates that the wavefunction is centered outside the atomic sites.
How can I obtain the correct polaron wavefunction? Thank you.
The version of EPW is 6.0.
*****************epw1.in
prefix = 'blue'
outdir = './'
elph = .true.
epwwrite = .true.
lpolar = .true.
nbndsub = 3
dvscf_dir = './save'
etf_mem = 0
bands_skipped = 'exclude_bands = 1-2, 6-20'
wannierize = .true.
num_iter = 500
iprint = 2
proj(1) = 'f=0.3333333330,0.6666666670,0.4705074384:p'
wdata(1) = 'use_ws_distance = T'
dis_win_min = -17
dis_win_max = -5
!dis_froz_min = -3
dis_froz_max = -5
!system_2d = 'dipole_sp'
wannier_plot = .true.
wannier_plot_supercell = 6 6 1
!wannier_plot_radius = 2
nk1 = 6
nk2 = 6
nk3 = 1
nq1 = 6
nq2 = 6
nq3 = 1
band_plot = .true.
filkf = './kpoints'
filqf = './kpoints'
/
******************************epw2.in
&inputepw
prefix = 'blue'
outdir = './'
elph = .true.
epwread = .true.
lpolar = .true.
nbndsub = 3
dvscf_dir = './save/'
!system_2d = 'dipole_sp'
etf_mem = 0
wannierize = .false.
plrn = .true.
restart_plrn = .false.
type_plrn = 1
init_plrn = 1
!init_ntau_plrn = 1
init_sigma_plrn = 1
niter_plrn = 100
conv_thr_plrn = 5E-4
ethrdg_plrn = 5E-4
!full_diagon_plrn = .true.
!adapt_ethrdg_plrn = .true.
nk1 = 6
nk2 = 6
nk3 = 1
nq1 = 6
nq2 = 6
nq3 = 1
nkf1 = 12
nkf2 = 12
nkf3 = 1
nqf1 = 12
nqf2 = 12
nqf3 = 1
/

[jlb]

Dear jack,

Thank you for your post.

The error "Non-physical solution, check initial guess and convergence" is issued as a safeguard to prevent unphysical results when there are atomic displacements that exceed half of the lattice parameter. This usually indicates that there’s a problem in your calculation.

Can you please share the scf, ph, and nscf input files you used prior to the EPW calculation, so that we can reproduce the error?

Best,
Jon Lafuente-Bartolome

[jack]

Dear,
Thank you for your response. I have uploaded all input files.
The wannierization is implied with the "wannier_plot_supercell = 6 6 2", and the proj is set to P's p orbit. The fitting bands agree well with the DFT.
The polaron I calcualted is hole polaron.