[Pw_forum] a question about MnSe

[mohnish pandey]

Dear QE users,
                           I am trying to do bulk calculations for MnSe in
rocksalt and wurtzite structure. Its has AFM ground state in rocksalt
structure but after checking convergence I am finding "rocksalt" structure
to be energetically higher than wurtzite structure. I am pasting my segments
of input and output files. Can anybody please help me in figuring out the
problem.

*INPUT FOR ROCKSALT*

&control
    calculation = 'vc-relax'
    restart_mode='restart',
    wf_collect = .true.
    prefix='mnse',
    pseudo_dir = '/home/mohnish/mnse-rocksalt-bulk',
    outdir='/home/mohnish/mnse-rocksalt-bulk',
    tprnfor = .true.,
    tstress=.true.
 /
 &system
    ibrav=  0, celldm(1)= 10.3026, nat=  4, ntyp= 3,
    ecutwfc = 40.0, ecutrho = 320.0,
    occupations='smearing', smearing='gauss', degauss=0.01,
    nspin=2,
    starting_magnetization(1)= 0.0,
    starting_magnetization(2)= 0.5,
    starting_magnetization(3)=-0.5,
 /
 &electrons
   diagonalization='david'
   mixing_mode = 'plain'
   mixing_beta = 0.4
   conv_thr = 1.0d-8
   startingpot = 'file'
   startingwfc = 'file'
 /
&IONS
  ion_dynamics='bfgs'
  trust_radius_max = 0.40
  trust_radius_ini = 0.20
/
&CELL
  cell_dynamics='bfgs',
/
ATOMIC_SPECIES
  Se  78.960 Se.pbe-van.UPF
  Mn1 54.938 Mn.pbe-sp-van_mit.UPF
  Mn2 54.938 Mn.pbe-sp-van_mit.UPF
CELL_PARAMETERS
0.50 0.50 1.00
0.50 1.00 0.50
1.00 0.50 0.50
ATOMIC_POSITIONS {crystal}
 Se  0.25 0.25 0.25
 Se  0.75 0.75 0.75
 Mn1 0.0  0.0  0.0
 Mn2 0.5  0.5  0.5
K_POINTS {automatic}
6 6 6 0 0 0

*OUTPUT FOR ROCKSALT*

 bfgs converged in   8 scf cycles and   4 bfgs steps
     (criteria: energy < 0.10E-03, force < 0.10E-02, cell < 0.50E+00)

     End of BFGS Geometry Optimization

     Final enthalpy =    -464.4688263706 Ry
Begin final coordinates
     new unit-cell volume =    533.55466 a.u.^3 (    79.06464 Ang^3 )

CELL_PARAMETERS (alat= 10.30260000)
   0.494008772   0.494008772   0.990589056
   0.494008772   0.990589056   0.494008772
   0.990589056   0.494008772   0.494008772

ATOMIC_POSITIONS (crystal)
Se       0.249999854   0.249999854   0.249999854
Se       0.750000146   0.750000146   0.750000146
Mn1      0.000000000   0.000000000   0.000000000
Mn2      0.500000000   0.500000000   0.500000000
End final coordinates

*INPUT FOR WURTZITE*

&control
    calculation = 'vc-relax',
    restart_mode='restart',
    verbosity = 'high'
    wf_collect = .true.
    outdir='/home/mohnish/mnse-wurtzite-bulk',
    pseudo_dir='/home/mohnish/mnse-wurtzite-bulk'
    prefix='mnse',
    tstress = .true.,
    tprnfor = .true.,
/
 &system
    ibrav=  4, a = 4.178, c = 6.783,nat= 4, ntyp= 3,
    ecutwfc =
40,ecutrho=320,occupations='smearing',degauss=0.01,smearing='gaussian',
    nspin =2,starting_magnetization(1)=0.5,starting_magnetization(2)= -0.5,
/
 &electrons
   diagonalization='david'
   mixing_mode = 'plain'
   mixing_beta = 0.4
   conv_thr = 1.0d-8
   startingpot = 'file'
   startingwfc = 'file'
 /
&IONS
  ion_dynamics='bfgs'
  trust_radius_max = 0.40
  trust_radius_ini = 0.20
/
&CELL
  cell_dynamics='bfgs',
/
ATOMIC_SPECIES
  Mn1 54.938 Mn.pbe-sp-van_mit.UPF
  Mn2 54.938 Mn.pbe-sp-van_mit.UPF
  Se  78.960 Se.pbe-van.UPF
ATOMIC_POSITIONS (crystal)
  Mn1  0.000000000  0.000000000000  0.000000000
  Mn2  0.333333333  0.666666666667  0.500000000
  Se   0.000000000  0.000000000000  0.345000000
  Se   0.333333333  0.666666666667  0.845000000
 K_POINTS (automatic)
 6 6 4 0 0 0

*OUTPUT FOR WURTZITE*

 End of BFGS Geometry Optimization

     Final enthalpy =    -464.4799667612 Ry
Begin final coordinates
     new unit-cell volume =    681.36082 a.u.^3 (   100.96726 Ang^3 )

CELL_PARAMETERS (alat=  7.89527578)
   1.001414763   0.000000000   0.000000000
  -0.500707382   0.867250625   0.000000000
   0.000000000   0.000000000   1.594103933

ATOMIC_POSITIONS (crystal)
Mn1      0.000000000   0.000000000  -0.014999731
Mn2      0.333333333   0.666666667   0.485592670
Se       0.000000000   0.000000000   0.359333481
Se       0.333333333   0.666666667   0.860073579
End final coordinates





-- 
Regards,
MOHNISH,
-----------------------------------------------------------------
Mohnish Pandey
Y6927262,5th Year dual degree student,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
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