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<big><big><big> Dear all,<br>
<br>
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.<br>
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:<br>
<br>
<small>1) pw.x < h2o.scf >scf.out<br>
2) pw.x < h2o.nscf >nscf.out<br>
3) wannier90.x -pp h2o <br>
4) pw2wannier90.x < h2o.pw2wan > pw2wan.out
<br>
5) wannier90.x h2o</small><br>
<br>
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.<br>
<br>
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.<br>
<br>
The polarizations, which I found, are:<br>
<small><br>
Methods | Polarizations (Debye)<br>
(1) tefield | 1.8179<br>
(2) WFs | 1.8966<br>
<br>
using 'relax' command:<br>
(3) tefield | 1.7828<br>
(4) WFs </small></big></big><small><big><big> | 1.8544</big></big><br>
</small></big>
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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.<br>
<br>
With best regards,
</big></big></big><br>
<big><big><big><br>
Pedro Moreira</big></big></big><br>
<br>
<big><big><big><small><small>##h2o.scf########################################<br>
&control<br>
calculation='scf', ! it was substituted
for 'nscf' and 'relax' in calculations with these names<br>
restart_mode='from_scratch',<br>
pseudo_dir='/home/pedro/Documentos/espresso-5.0/pseudo',<br>
outdir='/home/pedro/Documentos/espresso-5.0/exec1',<br>
prefix='h2o',<br>
tprnfor = .true.,<br>
nstep = 500,<br>
forc_conv_thr = 1.9e-4,<br>
tefield=.true.<br>
dipfield=.true.<br>
/<br>
&system<br>
ibrav = 0, <br>
nat = 3, ntyp = 2,<br>
ecutwfc = 70.0, ecutrho = 700.0,<br>
edir=3<br>
eamp=0.D0<br>
eopreg=0.1<br>
emaxpos=0.5<br>
/<br>
&electrons<br>
electron_maxstep = 500,<br>
/<br>
&ions<br>
/<br>
ATOMIC_SPECIES<br>
H 1.00790 H.blyp-van_ak.UPF<br>
O 15.9994 O.blyp-van_ak.UPF<br>
ATOMIC_POSITIONS angstrom<br>
O 0.0 0.0 0.0<br>
H 0.77 0.0 0.62<br>
H -0.77 0.0 0.62<br>
CELL_PARAMETERS angstrom<br>
10.6 0.00 0.00<br>
0.00 10.6 0.00<br>
0.00 0.00 10.6<br>
K_POINTS {gamma}<br>
##############################################</small></small><br>
</big></big>##scf.out#######################################<br>
iteration # 6 ecut= 70.00 Ry beta=0.70<br>
Davidson diagonalization with overlap<br>
ethr = 4.01E-07, avg # of iterations = 2.0<br>
<br>
</big>
<big>
negative rho (up, down): 0.293E-02 0.000E+00<br>
<br>
</big>
<big>
Adding external electric field<br>
<br>
</big>
<big>
Computed dipole along edir(3) : <br>
Dipole 0.7152 Ry au, 1.8179 Debye<br>
Dipole field 0.0011 Ry au<br>
<br>
</big>
<big>
Potential amp. -0.0403 Ry<br>
Total length 18.0280 bohr<br>
<br>
<br>
</big>
<big>
total cpu time spent up to now is 134.0 secs<br>
<br>
</big>
<big>
End of self-consistent calculation<br>
<br>
</big>
<big>
k = 0.0000 0.0000 0.0000 ( 39751 PWs) bands (ev):<br>
<br>
</big>
<big>
-24.8436 -12.5614 -9.1444 -7.1431<br>
<br>
! total energy = -34.42311963 Ry</big>
<big><br>
Harris-Foulkes estimate = -34.42315705 Ry<br>
estimated scf accuracy < 0.00000072 Ry<br>
##############################################<br>
##h2o.win######################################<br>
num_wann = 4 <br>
num_iter = 100<br>
<br>
begin atoms_cart<br>
O 0.0 0.0 0.0<br>
H 0.77 0.0 0.62<br>
H -0.77 0.0 0.62<br>
end atoms_cart<br>
<br>
begin projections<br>
random<br>
end projections<br>
<br>
begin unit_cell_cart<br>
10.6 0.00 0.00<br>
0.00 10.6 0.00<br>
0.00 0.00 10.6<br>
end unit_cell_cart<br>
<br>
mp_grid : 1 1 1 <br>
gamma_only : true<br>
<br>
begin kpoints<br>
0.0 0.0 0.0<br>
end kpoints<br>
##############################################<br>
##h2o.pw2wan##################################<br>
&inputpp <br>
outdir = './'<br>
prefix = 'h2o'<br>
seedname = 'h2o'<br>
spin_component = 'none'<br>
write_mmn = .true.<br>
write_amn = .true.<br>
write_unk = .false.<br>
/<br>
##############################################<br>
##h2o.wout_scf##################################<br>
Writing checkpoint file h2o.chk... done<br>
<br>
Final State<br>
WF centre and spread 1 ( -0.000000, -0.257416, -0.127263
) 0.53681556<br>
WF centre and spread 2 ( -0.399319, 0.000000, 0.338531
) 0.49244402<br>
WF centre and spread 3 ( 0.399320, -0.000000, 0.338532
) 0.49244441<br>
WF centre and spread 4 ( 0.000000, 0.257415, -0.127263
) 0.53681748<br>
Sum of centres and spreads ( 0.000001, -0.000001, 0.422537
) 2.05852147<br>
<br>
Spreads (Ang^2) Omega I = 1.816167784<br>
================ Omega D = 0.000000000<br>
Omega OD = 0.242353686<br>
Final Spread (Ang^2) Omega Total = 2.058521470<br>
------------------------------------------------------------------------------<br>
Time for wannierise 0.012 (sec)<br>
<br>
Writing checkpoint file h2o.chk... done<br>
##############################################<br>
##relax.out####################################<br>
Computed dipole along edir(3) : <br>
Dipole 0.7014 Ry au, 1.7828 Debye<br>
Dipole field 0.0011 Ry au<br>
<br>
Potential amp. -0.0395 Ry<br>
Total length 18.0280 bohr<br>
<br>
<br>
total cpu time spent up to now is 688.6 secs<br>
<br>
End of self-consistent calculation<br>
<br>
k = 0.0000 0.0000 0.0000 ( 39751 PWs) bands (ev):<br>
<br>
-24.9139 -12.7725 -9.0391 -7.1487<br>
<br>
! total energy = -34.42371576 Ry<br>
Harris-Foulkes estimate = -34.42371607 Ry<br>
estimated scf accuracy < 4.4E-10 Ry<br>
<br>
The total energy is the sum of the following terms:<br>
<br>
one-electron contribution = -64.27367874 Ry<br>
hartree contribution = 33.58470996 Ry<br>
xc contribution = -8.36936347 Ry<br>
ewald contribution = 4.63384732 Ry<br>
electric field correction = 0.00076917 Ry<br>
<br>
convergence has been achieved in 4 iterations<br>
<br>
Forces acting on atoms (Ry/au):<br>
<br>
atom 1 type 2 force = -0.00001778 0.00000017
0.00004093<br>
atom 2 type 1 force = -0.00002047 -0.00000010
-0.00001330<br>
atom 3 type 1 force = 0.00003825 -0.00000007
-0.00002763<br>
<br>
Total force = 0.000069 Total SCF correction =
0.000038<br>
SCF correction compared to forces is large: reduce conv_thr
to get better values<br>
<br>
bfgs converged in 6 scf cycles and 5 bfgs steps<br>
(criteria: energy < 0.10E-03, force < 0.19E-03)<br>
<br>
End of BFGS Geometry Optimization<br>
<br>
Final energy = -34.4237157619 Ry<br>
Begin final coordinates<br>
<br>
ATOMIC_POSITIONS (angstrom)<br>
O 0.000004575 -0.000000364 0.015670447<br>
H 0.774640336 0.000000070 0.612163521<br>
H -0.774644910 0.000000294 0.612166031<br>
End final coordinates<br>
#################################################<br>
##h2o.wout_relax###################################<br>
Writing checkpoint file h2o.chk... done<br>
<br>
Final State<br>
WF centre and spread 1 ( 0.000004, -0.255729, -0.113705
) 0.53766112<br>
WF centre and spread 2 ( -0.400232, 0.000000, 0.346762
) 0.48541250<br>
WF centre and spread 3 ( 0.400236, -0.000000, 0.346762
) 0.48540610<br>
WF centre and spread 4 ( 0.000005, 0.255727, -0.113705
) 0.53766277<br>
Sum of centres and spreads ( 0.000013, -0.000002, 0.466114
) 2.04614249<br>
<br>
Spreads (Ang^2) Omega I = 1.801532201<br>
================ Omega D = 0.000000000<br>
Omega OD = 0.244610290<br>
Final Spread (Ang^2) Omega Total = 2.046142491<br>
------------------------------------------------------------------------------<br>
##################################################<br>
</big><br>
<div class="moz-cite-prefix">
<pre><big><big><big>Em 29-06-2012 18:06, Pedro Augusto F. P. Moreira escreveu:</big></big></big></pre>
</div>
<blockquote cite="mid:4FEE18C6.5090906@ifi.unicamp.br" type="cite">
<pre wrap=""><big><big><big> 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
(<a class="moz-txt-link-freetext" href="http://www.democritos.it/pipermail/pw_forum/2009-March/011936.html">http://www.democritos.it/pipermail/pw_forum/2009-March/011936.html</a>) 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
</big></big></big></pre>
<big>
</big></blockquote>
<br>
<pre class="moz-signature" cols="72">--
Pedro Moreira
IFGW - Unicamp - Brazil</pre>
<br>
<br>
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