Dear Stefano,
<br> <br>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.
<br> <br>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?
<br> <br>&ELECTRONS
<br> diagonalization='david',
<br> conv_thr = 1.0d-8,
<br> mixing_beta = 0.5,
<br> startingwfc='random',
<br> efield_cart(1)=0.01
<br> efield_cart(2)=0.01
<br> efield_cart(3)=0.0
<br>/
<br>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?
<br> <br>Thanks,
<br>S. Sanchez
<br><br><br><div class="gmail_quote">On Mon, Aug 16, 2010 at 6:35 AM, Stefano de Gironcoli <span dir="ltr"><<a href="mailto:degironc@sissa.it">degironc@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
what are the forces when you DO NOT apply any electric field ?<br>
stefano<br>
<div><div></div><div class="h5"><br>
S. Sanchez wrote:<br>
> Dear all,<br>
><br>
><br>
><br>
> I have a question regarding the “lefield” keyword in PW.x code. I want to<br>
> understand why if apply a positive electric field along the x-direction<br>
> (0.01 a. u.) of a monoclinic crystal, and then, subsequently a negative<br>
> electric field (-0.01 a. u.) along the same x-direction, the atomic forces<br>
> (in Ry/a.u.) change not only their sign but as well their magnitude (see<br>
> below, specially atoms 7 to 12 along the x-coordinate). In previous<br>
> instances, I have applied positive and negative electric fields along the<br>
> x-direction of cubic crystalline systems, and basically, I have obtained the<br>
> same atomic forces but with different signs. In my understanding, even, if I<br>
> have a monoclinic crystal, changing the sign of an electric field should<br>
> only change the sign of the atomic forces, but not their magnitude; is this<br>
> correct?<br>
><br>
><br>
><br>
> Or what could be the reason for a change in both sign and magnitude of the<br>
> atomic forces, when one only changes the sign of the applied electric field<br>
> in monoclinic unit cells?<br>
><br>
><br>
><br>
> Thanks for your help,<br>
><br>
> S. Sanchez<br>
><br>
><br>
><br>
><br>
><br>
> Positive Electric Field Forces acting on atoms (Ry/au):<br>
><br>
><br>
><br>
> atom 1 type 2 force = 0.01368508 -0.00000463 -0.01954027<br>
><br>
> atom 2 type 2 force = 0.01368346 -0.00000528 0.01953860<br>
><br>
> atom 3 type 2 force = 0.01377590 -0.00017516 -0.04026512<br>
><br>
> atom 4 type 2 force = 0.01377535 -0.00017479 0.04026785<br>
><br>
> atom 5 type 2 force = 0.01376076 0.00016477 0.04122506<br>
><br>
> atom 6 type 2 force = 0.01376443 0.00016449 -0.04122388<br>
><br>
> atom 7 type 1 force = -0.05248836 0.00005249 0.00000005<br>
><br>
> atom 8 type 1 force = 0.00550320 -0.03398525 0.00000010<br>
><br>
> atom 9 type 1 force = 0.00562059 0.03391232 0.00000004<br>
><br>
> atom 10 type 1 force = 0.01308273 0.00010950 -0.00000080<br>
><br>
> atom 11 type 1 force = -0.02716328 0.02288385 -0.00000081<br>
><br>
> atom 12 type 1 force = -0.02699986 -0.02294231 -0.00000081<br>
><br>
><br>
><br>
><br>
><br>
> Negative Electric Field Forces acting on atoms (Ry/au):<br>
><br>
><br>
><br>
> atom 1 type 2 force = -0.01378038 -0.00000119 -0.01953455<br>
><br>
> atom 2 type 2 force = -0.01378055 -0.00000160 0.01953552<br>
><br>
> atom 3 type 2 force = -0.01374417 0.00011193 -0.04120520<br>
><br>
> atom 4 type 2 force = -0.01374465 0.00011173 0.04120524<br>
><br>
> atom 5 type 2 force = -0.01375505 -0.00012449 0.04022320<br>
><br>
> atom 6 type 2 force = -0.01375511 -0.00012497 -0.04022321<br>
><br>
> atom 7 type 1 force = -0.02545779 -0.00007625 -0.00000018<br>
><br>
> atom 8 type 1 force = 0.03331831 -0.03352278 -0.00000019<br>
><br>
> atom 9 type 1 force = 0.03321440 0.03357830 -0.00000017<br>
><br>
> atom 10 type 1 force = 0.04024209 -0.00008227 -0.00000015<br>
><br>
> atom 11 type 1 force = 0.00070042 0.02328288 -0.00000014<br>
><br>
> atom 12 type 1 force = 0.00054247 -0.02315129 -0.00000018<br>
><br>
><br>
><br>
> Here is the related Quantum Espresso input file:<br>
><br>
><br>
><br>
> &CONTROL<br>
><br>
> calculation='scf'<br>
><br>
> restart_mode='from_scratch',<br>
><br>
> prefix='na2o2',<br>
><br>
> lelfield=.true.,<br>
><br>
> nberrycyc=1<br>
><br>
> pseudo_dir='$PSEUDO_DIR/',<br>
><br>
> wf_collect=.true.,<br>
><br>
> verbosity='high',<br>
><br>
> tprnfor=.true.,<br>
><br>
> outdir='./'<br>
><br>
> /<br>
><br>
><br>
><br>
> &SYSTEM<br>
><br>
> ibrav = 0,<br>
><br>
> a=1,<br>
><br>
> nat =12,<br>
><br>
> ntyp =2,<br>
><br>
> ecutwfc = 80,<br>
><br>
> ecutrho = 320,<br>
><br>
> /<br>
><br>
><br>
><br>
> &ELECTRONS<br>
><br>
> diagonalization='david',<br>
><br>
> conv_thr = 1.0d-8,<br>
><br>
> mixing_beta = 0.5,<br>
><br>
> startingwfc='random',<br>
><br>
> efield_cart(3)=0.0<br>
><br>
> efield_cart(2)=0.0<br>
><br>
> efield_cart(1)=0.01 -ŕ Change sign accordingly between 0.01 or -0.01<br>
><br>
> /<br>
><br>
><br>
><br>
> CELL_PARAMETERS (alat)<br>
><br>
> 6.2199997902 0.0000000000 0.0000000000<br>
><br>
> -3.1099998951 5.3866778298 0.0000000000<br>
><br>
> 0.0000000000 0.0000000000 4.4699997902<br>
><br>
><br>
><br>
> ATOMIC_SPECIES<br>
><br>
> Na 23 Na.pz-n-vbc.UPF<br>
><br>
> O 16.0 O.pz-mt.UPF<br>
><br>
><br>
><br>
> ATOMIC_POSITIONS (crystal)<br>
><br>
> O 0.000000000 0.000000000 0.166999996<br>
><br>
> O 0.000000000 0.000000000 0.833000004<br>
><br>
> O 0.333333343 0.666666687 0.333000004<br>
><br>
> O 0.333333343 0.666666687 0.666999996<br>
><br>
> O 0.666666687 0.333333343 0.666999996<br>
><br>
> O 0.666666687 0.333333343 0.333000004<br>
><br>
> Na 0.723999977 0.000000000 0.500000000<br>
><br>
> Na 0.000000000 0.723999977 0.500000000<br>
><br>
> Na 0.276000023 0.276000023 0.500000000<br>
><br>
> Na 0.365999997 0.000000000 0.000000000<br>
><br>
> Na 0.000000000 0.365999997 0.000000000<br>
><br>
> Na 0.634000003 0.634000003 0.000000000<br>
><br>
><br>
><br>
> K_POINTS {automatic}<br>
><br>
> 2 2 2 0 0 0<br>
><br>
><br>
</div></div>> ------------------------------------------------------------------------<br>
><br>
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</blockquote></div><br>