[Wannier] Polarization of isolated H20 (dipole moment)

Pedro Augusto F. P. Moreira pmoreira at ifi.unicamp.br
Mon Jul 2 20:42:01 CEST 2012


  Dear all,

  I have not calculated correctly yet the spontaneous polarization of a 
water molecule as I mentioned in my last e-mail. Here, I gonna detail my 
calculation steps and put my inputs and main output and hope that 
someone could give any advice.
  As I said, I did two simulation: (1) as Cantele suggested: my h2o.scf 
input  had tefield=.true. (it can be seen below); (2) And using th 
Wannier funciton centres which I calculated with following sequence of 
commands:

1) pw.x < h2o.scf >scf.out
2) pw.x < h2o.nscf >nscf.out
3) wannier90.x -pp h2o
4) pw2wannier90.x < h2o.pw2wan > pw2wan.out
5) wannier90.x h2o

My inputs and main outputs are bellow. The polarization, using WFs, were 
calculated by the vectorial sum of ion positions times their atomic 
number less twice the WF centre sum.

  I repeated all calculations, using a "relax" command instead of "scf" 
command in step 1. The positions used on the following inputs (h2o.nscf, 
h2o.win and WF polarization calculations) were the relaxed atomic positions.

  The polarizations, which I found, are:

   Methods  |   Polarizations (Debye)
  (1) tefield |    1.8179
  (2) WFs    |    1.8966

  using 'relax' command:
  (3) tefield |    1.7828
  (4) WFs    |    1.8544

  Anyone knows why the polarization values are so discrepant. I note 
that the discrepancies are greater if the atoms are dislocated to the 
center of the cubic cell.

   With best regards,

   Pedro Moreira

##h2o.scf########################################
&control
     calculation='scf',              ! it was substituted for 'nscf' and 
'relax' in calculations with these names
     restart_mode='from_scratch',
pseudo_dir='/home/pedro/Documentos/espresso-5.0/pseudo',
     outdir='/home/pedro/Documentos/espresso-5.0/exec1',
     prefix='h2o',
     tprnfor = .true.,
     nstep = 500,
     forc_conv_thr = 1.9e-4,
     tefield=.true.
     dipfield=.true.
/
&system
     ibrav = 0,
     nat = 3, ntyp = 2,
     ecutwfc = 70.0, ecutrho = 700.0,
     edir=3
     eamp=0.D0
     eopreg=0.1
     emaxpos=0.5
/
&electrons
     electron_maxstep = 500,
/
&ions
/
ATOMIC_SPECIES
  H 1.00790 H.blyp-van_ak.UPF
  O 15.9994 O.blyp-van_ak.UPF
ATOMIC_POSITIONS angstrom
O    0.0  0.0  0.0
H    0.77 0.0  0.62
H   -0.77 0.0  0.62
CELL_PARAMETERS angstrom
    10.6  0.00  0.00
    0.00  10.6  0.00
    0.00  0.00  10.6
K_POINTS {gamma}
##############################################
##scf.out#######################################
      iteration #  6     ecut=    70.00 Ry     beta=0.70
      Davidson diagonalization with overlap
      ethr =  4.01E-07,  avg # of iterations =  2.0

      negative rho (up, down):  0.293E-02 0.000E+00

      Adding external electric field

      Computed dipole along edir(3) :
         Dipole                0.7152 Ry au,          1.8179 Debye
         Dipole field          0.0011 Ry au

         Potential amp.       -0.0403 Ry
         Total length         18.0280 bohr


      total cpu time spent up to now is      134.0 secs

      End of self-consistent calculation

           k = 0.0000 0.0000 0.0000 ( 39751 PWs)   bands (ev):

    -24.8436 -12.5614  -9.1444  -7.1431

!    total energy              =     -34.42311963 Ry
      Harris-Foulkes estimate   =     -34.42315705 Ry
      estimated scf accuracy    <       0.00000072 Ry
##############################################
##h2o.win######################################
num_wann        =  4
num_iter        = 100

begin atoms_cart
O    0.0  0.0  0.0
H    0.77 0.0  0.62
H   -0.77 0.0  0.62
end atoms_cart

begin projections
random
end projections

begin unit_cell_cart
    10.6  0.00  0.00
    0.00  10.6  0.00
    0.00  0.00  10.6
end unit_cell_cart

mp_grid    : 1 1 1
gamma_only : true

begin kpoints
0.0 0.0 0.0
end kpoints
##############################################
##h2o.pw2wan##################################
&inputpp
    outdir = './'
    prefix = 'h2o'
    seedname = 'h2o'
    spin_component = 'none'
    write_mmn = .true.
    write_amn = .true.
    write_unk = .false.
/
##############################################
##h2o.wout_scf##################################
  Writing checkpoint file h2o.chk... done

  Final State
   WF centre and spread    1  ( -0.000000, -0.257416, -0.127263 )     
0.53681556
   WF centre and spread    2  ( -0.399319,  0.000000,  0.338531 )     
0.49244402
   WF centre and spread    3  (  0.399320, -0.000000,  0.338532 )     
0.49244441
   WF centre and spread    4  (  0.000000,  0.257415, -0.127263 )     
0.53681748
   Sum of centres and spreads (  0.000001, -0.000001,  0.422537 )     
2.05852147

          Spreads (Ang^2)       Omega I      =     1.816167784
         ================       Omega D      =     0.000000000
                                Omega OD     =     0.242353686
     Final Spread (Ang^2)       Omega Total  =     2.058521470
  ------------------------------------------------------------------------------
  Time for wannierise            0.012 (sec)

  Writing checkpoint file h2o.chk... done
##############################################
##relax.out####################################
      Computed dipole along edir(3) :
         Dipole                0.7014 Ry au,          1.7828 Debye
         Dipole field          0.0011 Ry au

         Potential amp.       -0.0395 Ry
         Total length         18.0280 bohr


      total cpu time spent up to now is      688.6 secs

      End of self-consistent calculation

           k = 0.0000 0.0000 0.0000 ( 39751 PWs)   bands (ev):

    -24.9139 -12.7725  -9.0391  -7.1487

!    total energy              =     -34.42371576 Ry
      Harris-Foulkes estimate   =     -34.42371607 Ry
      estimated scf accuracy    <          4.4E-10 Ry

      The total energy is the sum of the following terms:

      one-electron contribution =     -64.27367874 Ry
      hartree contribution      =      33.58470996 Ry
      xc contribution           =      -8.36936347 Ry
      ewald contribution        =       4.63384732 Ry
      electric field correction =       0.00076917 Ry

      convergence has been achieved in   4 iterations

      Forces acting on atoms (Ry/au):

      atom    1 type  2   force =    -0.00001778    0.00000017 0.00004093
      atom    2 type  1   force =    -0.00002047   -0.00000010 -0.00001330
      atom    3 type  1   force =     0.00003825   -0.00000007 -0.00002763

      Total force =     0.000069     Total SCF correction = 0.000038
      SCF correction compared to forces is large: reduce conv_thr to get 
better values

      bfgs converged in   6 scf cycles and   5 bfgs steps
      (criteria: energy < 0.10E-03, force < 0.19E-03)

      End of BFGS Geometry Optimization

      Final energy   =     -34.4237157619 Ry
Begin final coordinates

ATOMIC_POSITIONS (angstrom)
O        0.000004575  -0.000000364   0.015670447
H        0.774640336   0.000000070   0.612163521
H       -0.774644910   0.000000294   0.612166031
End final coordinates
#################################################
##h2o.wout_relax###################################
Writing checkpoint file h2o.chk... done

  Final State
   WF centre and spread    1  (  0.000004, -0.255729, -0.113705 )     
0.53766112
   WF centre and spread    2  ( -0.400232,  0.000000,  0.346762 )     
0.48541250
   WF centre and spread    3  (  0.400236, -0.000000,  0.346762 )     
0.48540610
   WF centre and spread    4  (  0.000005,  0.255727, -0.113705 )     
0.53766277
   Sum of centres and spreads (  0.000013, -0.000002,  0.466114 )     
2.04614249

          Spreads (Ang^2)       Omega I      =     1.801532201
         ================       Omega D      =     0.000000000
                                Omega OD     =     0.244610290
     Final Spread (Ang^2)       Omega Total  =     2.046142491
  ------------------------------------------------------------------------------
##################################################

Em 29-06-2012 18:06, Pedro Augusto F. P. Moreira escreveu:

>    Dear all.
>
>    I am trying to calculate the spontaneous electric polarization of a
> single water molecule as a test.
>    I am using Quantum Espresso (pw.x and wannier90). I did by two
> methods:  (1) using  tefield=.true. as suggested by Cantele
> (http://www.democritos.it/pipermail/pw_forum/2009-March/011936.html) and
> (2) by Wannier function centres (WF).
>    I run a set of simulations with different initial atomic positions.
> The first simulation, I used the positions mentioned by Cantele and
> found P = 1.82 D and P =1.84 D by method (1). By WF, P= 1.90 D and 1.92
> D. The first values are calculated with BLYP functional and the second
> ones with PBE functional.
>    After that, I moved initially all atoms by a vector (1.0  0.0  0.0)
> angstrom, relaxed the molecule and did again the calculations above. I
> found for Cantele way: P = 1.78 D and 1.80 D. By WF, P = 6.33 D and 6.37 D.
>    My questions are:
>
>    (a) I expected to find values closer to 1.87 D in all calculations,
> but all they are diverging from this value by, at least, 2 %. Should I
> really expect it ?
>    (b) Anyone knows what can be happening in WF calculations when I moved
> the atoms? I know that if the atoms were moved beyond the unit cell, a
> constant factor would be summed to polarization. But, I think that is
> not my case because the dislocation vector was 1.0 A , while my cubic
> cell has 10.6 A edges.
>
>    With best regards,
>
>    Pedro
>

-- 
Pedro Moreira

IFGW - Unicamp - Brazil



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