[Pw_forum] Large band gap in MnWO4

[Dr. Raghavender A T]

Dear Experts,

For the first time I am working on DFT that too by using quantum espresso
software. I am trying to do DFT calculations on MnWO4 bulk materials to
study the magnetic and structural properties using espresso-5.1 version.

With the MnWO4.scf.in file ( see the attachment), I got the magnetization
value as  4.58 Bohr mag/cell similar to that observed in literature.

However, when I am trying to calculate the band gap, always I am getting
band gap around 8eV. Where as the expected band gap is in the range of 3
eV. I made several trails with MnWO4 input using different pseudopotentials
in LDA+U and GGA+U mode.

Referring to literature I gave U values for Mn = 3.9 - 4.0 eV, W = 6.2 eV
and O = 6.5 eV. I have also introduced nqx1, nqx2 and nqx3 different
values. But there is no improvement in the bad gap energy.

I gave ibrav = -12 as it is monoclinic stricture and specified Celldm(2),
Celldm(3), and Celldm(5) with the corresponding values (not included here)
but it is giving error.

I suspect there is some missing parameter in the input file, which I am
unable to fix. Please have a look into the input file and pass me your
suggestions to improve my band gap calculations.

The input file attached is the one for which I got the magnetization value
as  4.58 Bohr mag/cell.

MnWO4.scf.in
&CONTROL
                 calculation = 'scf' ,
                restart_mode = 'from_scratch' ,
                  wf_collect = .true. ,
                      outdir =
'/home/hamshu/Downloads/espresso-5.1/tempdir/' ,
                      wfcdir =
'/home/hamshu/Downloads/espresso-5.1/tempdir/' ,
                  pseudo_dir =
'/home/hamshu/Downloads/espresso-5.1/pseudo/' ,
                      prefix = 'MnWO4' ,
                 lkpoint_dir = .true. ,
                     disk_io = 'high' ,
                   verbosity = 'high' ,
 /
 &SYSTEM
                       ibrav = 0,
                         nat = 12,
                        ntyp = 3,
                     ecutwfc = 30 ,
                     ecutrho = 240 ,
                        nbnd = 84,
                  tot_charge = 0.000000,
                 occupations = 'smearing' ,
                     degauss = 0.001 ,
                    smearing = 'marzari-vanderbilt' ,
                       nspin = 2 ,
   starting_magnetization(1) = 0.5,
            exxdiv_treatment = 'gygi-baldereschi' ,
                  lda_plus_u = .true. ,
             lda_plus_u_kind = 1 ,
                Hubbard_U(1) = 4.0,
           U_projection_type = 'ortho-atomic' ,
 /
 &ELECTRONS
           scf_must_converge = .true. ,
                    conv_thr = 1.0d-8 ,
                 mixing_mode = 'plain' ,
                 mixing_beta = 0.05 ,
             diagonalization = 'david' ,
 /
CELL_PARAMETERS bohr
     9.133754000    0.000000000    0.000000000
     0.000000000   10.889400000    0.000000000
    -0.186425164    0.000000000    9.442959954
ATOMIC_SPECIES
   Mn   54.93800  mn_lda_v1.2.uspp.F.UPF
    O   15.99900  o_lda_v1.2.uspp.F.UPF
    W  183.84000  w_lda_v1.2.uspp.F.UPF
ATOMIC_POSITIONS crystal
   Mn      0.500000000    0.653000000    0.250000000
   Mn      0.500000000    0.347000000    0.750000000
    W      0.000000000    0.180000000    0.250000000
    W      0.000000000    0.820000000    0.750000000
    O      0.220000000    0.110000000    0.960000000
    O      0.780000000    0.890000000    0.040000000
    O      0.780000000    0.110000000    0.540000000
    O      0.220000000    0.890000000    0.460000000
    O      0.260000000    0.380000000    0.390000000
    O      0.740000000    0.620000000    0.610000000
    O      0.740000000    0.380000000    0.110000000
    O      0.260000000    0.620000000    0.890000000
K_POINTS automatic
  4 6 8   0 0 0


Thanking ou
Regards


*Raghavender A T*

*Postdoctoral Fellow,*

*Nanomagnetism Laboratory,*

*Department of Physics and Astronomy,*

*Seoul National University,*

*Seoul, South Korea.*

*Email:         raghavi9 at gmail.com <raghavi9 at gmail.com>, raghavi9 at yahoo.com
<raghavi9 at yahoo.com>*
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