[Pw_forum] resulting atomic forces when using the "lefield" tag
S. Sanchez
lcqsigi at gmail.com
Mon Aug 16 18:26:34 CEST 2010
Dear Stefano,
I understand your point regarding the optimization of the unit cell and
atomic positions before utilizing the "lefield" tag. Indeed, by optimizing
my system, I was able to obtain the same magnitude of the atomic forces
along the x-coordinate, but with different sings upon changing the sign of
the electric field.
Now, if you were to apply an electric along a diagonal direction in a
monoclinic crystal (where beta = 120 degrees), can one decompose this
diagonal electric field (in the XY quadrant) into its respective X and Y
components? In other words, will it be possible to apply two electric fields
using the PW.x code in monoclinic unit cells?
&ELECTRONS
diagonalization='david',
conv_thr = 1.0d-8,
mixing_beta = 0.5,
startingwfc='random',
efield_cart(1)=0.01
efield_cart(2)=0.01
efield_cart(3)=0.0
/
Also, given the fact that the monoclinic unit cell under study has an angle
beta = 120 degrees, it will make sense to rotate the unit-cell parameters
(i.e., a, b, c, alpha, beta, gamma) and the atomic positions by 60 degrees
(along the z-axis) to align a diagonal electric field (in the XY quadrant)
along the x-direction of the rotated system; will a rotation like this be
enough to capture the response of a diagonal electric field in a monoclinic
unit cell? Or should I be aware of other details regarding the
implementation of electric fields in non-cubic unit cells?
Thanks,
S. Sanchez
On Mon, Aug 16, 2010 at 6:35 AM, Stefano de Gironcoli <degironc at sissa.it>wrote:
> what are the forces when you DO NOT apply any electric field ?
> stefano
>
> S. Sanchez wrote:
> > Dear all,
> >
> >
> >
> > I have a question regarding the “lefield” keyword in PW.x code. I want to
> > understand why if apply a positive electric field along the x-direction
> > (0.01 a. u.) of a monoclinic crystal, and then, subsequently a negative
> > electric field (-0.01 a. u.) along the same x-direction, the atomic
> forces
> > (in Ry/a.u.) change not only their sign but as well their magnitude (see
> > below, specially atoms 7 to 12 along the x-coordinate). In previous
> > instances, I have applied positive and negative electric fields along the
> > x-direction of cubic crystalline systems, and basically, I have obtained
> the
> > same atomic forces but with different signs. In my understanding, even,
> if I
> > have a monoclinic crystal, changing the sign of an electric field should
> > only change the sign of the atomic forces, but not their magnitude; is
> this
> > correct?
> >
> >
> >
> > Or what could be the reason for a change in both sign and magnitude of
> the
> > atomic forces, when one only changes the sign of the applied electric
> field
> > in monoclinic unit cells?
> >
> >
> >
> > Thanks for your help,
> >
> > S. Sanchez
> >
> >
> >
> >
> >
> > Positive Electric Field Forces acting on atoms (Ry/au):
> >
> >
> >
> > atom 1 type 2 force = 0.01368508 -0.00000463
> -0.01954027
> >
> > atom 2 type 2 force = 0.01368346 -0.00000528
> 0.01953860
> >
> > atom 3 type 2 force = 0.01377590 -0.00017516
> -0.04026512
> >
> > atom 4 type 2 force = 0.01377535 -0.00017479
> 0.04026785
> >
> > atom 5 type 2 force = 0.01376076 0.00016477
> 0.04122506
> >
> > atom 6 type 2 force = 0.01376443 0.00016449
> -0.04122388
> >
> > atom 7 type 1 force = -0.05248836 0.00005249
> 0.00000005
> >
> > atom 8 type 1 force = 0.00550320 -0.03398525
> 0.00000010
> >
> > atom 9 type 1 force = 0.00562059 0.03391232
> 0.00000004
> >
> > atom 10 type 1 force = 0.01308273 0.00010950
> -0.00000080
> >
> > atom 11 type 1 force = -0.02716328 0.02288385
> -0.00000081
> >
> > atom 12 type 1 force = -0.02699986 -0.02294231
> -0.00000081
> >
> >
> >
> >
> >
> > Negative Electric Field Forces acting on atoms (Ry/au):
> >
> >
> >
> > atom 1 type 2 force = -0.01378038 -0.00000119
> -0.01953455
> >
> > atom 2 type 2 force = -0.01378055 -0.00000160
> 0.01953552
> >
> > atom 3 type 2 force = -0.01374417 0.00011193
> -0.04120520
> >
> > atom 4 type 2 force = -0.01374465 0.00011173
> 0.04120524
> >
> > atom 5 type 2 force = -0.01375505 -0.00012449
> 0.04022320
> >
> > atom 6 type 2 force = -0.01375511 -0.00012497
> -0.04022321
> >
> > atom 7 type 1 force = -0.02545779 -0.00007625
> -0.00000018
> >
> > atom 8 type 1 force = 0.03331831 -0.03352278
> -0.00000019
> >
> > atom 9 type 1 force = 0.03321440 0.03357830
> -0.00000017
> >
> > atom 10 type 1 force = 0.04024209 -0.00008227
> -0.00000015
> >
> > atom 11 type 1 force = 0.00070042 0.02328288
> -0.00000014
> >
> > atom 12 type 1 force = 0.00054247 -0.02315129
> -0.00000018
> >
> >
> >
> > Here is the related Quantum Espresso input file:
> >
> >
> >
> > &CONTROL
> >
> > calculation='scf'
> >
> > restart_mode='from_scratch',
> >
> > prefix='na2o2',
> >
> > lelfield=.true.,
> >
> > nberrycyc=1
> >
> > pseudo_dir='$PSEUDO_DIR/',
> >
> > wf_collect=.true.,
> >
> > verbosity='high',
> >
> > tprnfor=.true.,
> >
> > outdir='./'
> >
> > /
> >
> >
> >
> > &SYSTEM
> >
> > ibrav = 0,
> >
> > a=1,
> >
> > nat =12,
> >
> > ntyp =2,
> >
> > ecutwfc = 80,
> >
> > ecutrho = 320,
> >
> > /
> >
> >
> >
> > &ELECTRONS
> >
> > diagonalization='david',
> >
> > conv_thr = 1.0d-8,
> >
> > mixing_beta = 0.5,
> >
> > startingwfc='random',
> >
> > efield_cart(3)=0.0
> >
> > efield_cart(2)=0.0
> >
> > efield_cart(1)=0.01 -à Change sign accordingly between 0.01 or -0.01
> >
> > /
> >
> >
> >
> > CELL_PARAMETERS (alat)
> >
> > 6.2199997902 0.0000000000 0.0000000000
> >
> > -3.1099998951 5.3866778298 0.0000000000
> >
> > 0.0000000000 0.0000000000 4.4699997902
> >
> >
> >
> > ATOMIC_SPECIES
> >
> > Na 23 Na.pz-n-vbc.UPF
> >
> > O 16.0 O.pz-mt.UPF
> >
> >
> >
> > ATOMIC_POSITIONS (crystal)
> >
> > O 0.000000000 0.000000000 0.166999996
> >
> > O 0.000000000 0.000000000 0.833000004
> >
> > O 0.333333343 0.666666687 0.333000004
> >
> > O 0.333333343 0.666666687 0.666999996
> >
> > O 0.666666687 0.333333343 0.666999996
> >
> > O 0.666666687 0.333333343 0.333000004
> >
> > Na 0.723999977 0.000000000 0.500000000
> >
> > Na 0.000000000 0.723999977 0.500000000
> >
> > Na 0.276000023 0.276000023 0.500000000
> >
> > Na 0.365999997 0.000000000 0.000000000
> >
> > Na 0.000000000 0.365999997 0.000000000
> >
> > Na 0.634000003 0.634000003 0.000000000
> >
> >
> >
> > K_POINTS {automatic}
> >
> > 2 2 2 0 0 0
> >
> >
> > ------------------------------------------------------------------------
> >
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
> >
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20100816/005a1c86/attachment.html>
More information about the users
mailing list