Dear Mohamed,<br><br>This is one example:<br>- In &control: You should add<br> tefield = .true.<br> dipfield = .true. <br>The second is dipole correction <br>- In &system, you should add<br> edir = 3 ! This is the direction of applied field<br>
eamp = 0.002 ! Amplitude of e-field-should be small<br> emaxpos = 0.9 <br>
eopreg = 0.2<br>In this way, the potential increase from (emaxpos+eopreg-1)=0.1 to (emaxpos) = 0.9 <br>then decrease to 0 until (emaxpos+eopreg)=1.1 (in the units of the crystal vector edir). <br>You can draw this to see why it is called sawtooth potential. <br>
It is better to have your system in the middle of the super-cell, and the vacuum<br>region should be large enough so that you can <b>make sure</b> that your system lies between<br>(emaxpos+eopreg-1) and (emaxpos+eopreg).<br>
The change of slope <b>must</b> be in the vacuum region. <br>You can find some more information here: R. Resta and K. Kunc, Phys. Rev. B 34, 7146 (1986)<br><br>Good luck,<br><br><div class="gmail_quote">On Wed, Dec 16, 2009 at 2:24 PM, mohamed sabri majdoub <span dir="ltr"><<a href="mailto:majdoub@gmail.com">majdoub@gmail.com</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;">Dear users,<br><br>I was reading the documentation for the saw tooth like potential in pwscf.<br>
However, I still did not understood it in full. Can anybody gives me more details about how the potential is implemented.<br>
I need to apply an electric field to a supercell of graphene and BN layers with both ends in vacuum. eamp = 0.002. <pre><font size="4"><br>Amplitude of the electric field (in a.u. = 51.44 10^10 V/m )<br>The sawlike potential increases with slope "eamp" in the<br>
region from (emaxpos+eopreg-1) to (emaxpos), then decreases<br>to 0 until (emaxpos+eopreg), in units of the crystal<br>vector "edir". <span style="background-color: rgb(255, 255, 0);">Important: the change of slope of this</span><br style="background-color: rgb(255, 255, 0);">
<span style="background-color: rgb(255, 255, 0);">potential must be located in the empty region, or else</span><br style="background-color: rgb(255, 255, 0);"><span style="background-color: rgb(255, 255, 0);">unphysical forces will result. Used only if tefield is .TRUE.</span></font><br>
</pre>The following keywords that need to be used are still not clear. In particular the position of the slope change.Does it need to be in vacuum?<br>emaxpos=0.5 (Position of the maximum of the sawlike potential along crystal <font size="2">axis "edir"</font>); eopreg=0.5 (Zone in the unit cell where the sawlike potential decreases.)?<br>
How the sawlike potential is modeled.<br>Thank you in advance for your help and comment.<br><br>Here is the system I want to apply electric field to it:<br><br>&control<br> title = 'GphBN'<br> calculation = 'relax'<br>
outdir = '/pwscf/pwscftemp/relaxGphBN'<br> prefix = 'GphBN'<br> pseudo_dir = /pwscf/input/Gph-BN/pseudopot-C-B-N'<br> verbosity = 'high'<br> tprnfor = .t.<br>
restart_mode = 'from_scratch'<br><br> / <br> &system<br> ibrav = 0,<br> celldm(1) = 1.8897261<br> nat = 72,<br> ntyp = 3,<br> ecutwfc = 25.0<br> ecutrho = 250.0<br>
occupations = 'smearing'<br> smearing = 'gaussian'<br> degauss = 0.003675<br><br> /<br> &electrons<br> mixing_beta = 0.05<br> diagonalization = 'david'<br><br> /<br>
&ions<br> trust_radius_ini = 0.10<br><br> /<br> &cell<br> <br>ATOMIC_SPECIES<br> B 10.81100 B.pz-vbc.UPF<br> C 12.01070 C.pz-vbc.UPF<br> N 14.00674 N.pz-vbc.UPF<br>ATOMIC_POSITIONS angstrom<br> B 0.710000 8.607000 11.306000<br>
B 0.710000 11.066000 11.306000<br> B 2.840000 7.377000 11.306000<br> B 0.710000 6.148000 11.306000<br> B 6.390000 6.148000 8.000000<br>
B 6.390000 8.607000 8.000000<br>
B 6.390000 11.066000 8.000000<br> B 2.840000 9.836000 11.306000<br> B 7.100000 7.377000 11.306000<br> B 7.100000 9.836000 11.306000<br>
B 7.100000 12.295000 11.306000<br>
B 4.970000 11.066000 11.306000<br> B 2.840000 12.295000 11.306000<br> B 4.970000 6.148000 11.306000<br> B 4.970000 8.607000 11.306000<br>
B 4.260000 7.377000 8.000000<br>
B 2.130000 11.066000 8.000000<br> B 2.130000 8.607000 8.000000<br> B 2.130000 6.148000 8.000000<br> B 4.260000 9.836000 8.000000<br>
B 0.000000 7.377000 8.000000<br>
B 0.000000 9.836000 8.000000<br> B 4.260000 12.295000 8.000000<br> B 0.000000 12.295000 8.000000<br> C 2.130000 6.148000 14.612000<br>
C 2.130000 8.607000 14.612000<br>
C 2.130000 11.066000 14.612000<br> C 0.000000 12.295000 14.612000<br> C 0.000000 9.836000 14.612000<br> C 0.000000 7.377000 14.612000<br>
C 0.710000 11.066000 14.612000<br>
C 0.710000 8.607000 14.612000<br> C 0.710000 6.148000 14.612000<br> C 6.390000 8.607000 14.612000<br> C 6.390000 6.148000 14.612000<br>
C 4.970000 11.066000 14.612000<br>
C 6.390000 11.066000 14.612000<br> C 7.100000 12.295000 14.612000<br> C 7.100000 9.836000 14.612000<br> C 7.100000 7.377000 14.612000<br>
C 4.970000 8.607000 14.612000<br>
C 2.840000 12.295000 14.612000<br> C 2.840000 9.836000 14.612000<br> C 2.840000 7.377000 14.612000<br> C 4.260000 7.377000 14.612000<br>
C 4.970000 6.148000 14.612000<br>
C 4.260000 12.295000 14.612000<br> C 4.260000 9.836000 14.612000<br> N 0.000000 12.295000 11.306000<br> N 0.000000 9.836000 11.306000<br>
N 0.000000 7.377000 11.306000<br>
N 2.840000 7.377000 8.000000<br> N 2.840000 9.836000 8.000000<br> N 2.840000 12.295000 8.000000<br> N 4.970000 11.066000 8.000000<br>
N 4.970000 8.607000 8.000000<br>
N 4.970000 6.148000 8.000000<br> N 7.100000 12.295000 8.000000<br> N 7.100000 9.836000 8.000000<br> N 7.100000 7.377000 8.000000<br>
N 0.710000 6.148000 8.000000<br>
N 0.710000 8.607000 8.000000<br> N 0.710000 11.066000 8.000000<br> N 6.390000 11.066000 11.306000<br> N 6.390000 8.607000 11.306000<br>
N 6.390000 6.148000 11.306000<br>
N 2.130000 11.066000 11.306000<br> N 2.130000 8.607000 11.306000<br> N 2.130000 6.148000 11.306000<br> N 4.260000 12.295000 11.306000<br>
N 4.260000 9.836000 11.306000<br>
N 4.260000 7.377000 11.306000<br>K_POINTS automatic<br>10 10 1 1 1 0 <br>CELL_PARAMETERS<br>8.51980 0.00000 0.00000<br>0.00000 7.37600 0.00000<br>0.00000 0.00000 22.6120<br><br><br>
<br>_______________________________________________<br>
Pw_forum mailing list<br>
<a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
<a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>
<br></blockquote></div><br><br clear="all"><br>-- <br>Tuan Anh Pham<br>Department of Chemistry<br>University of California, Davis<br>Phone: 530-752-0957<br>Homepage: <a href="http://angstrom.ucdavis.edu/">http://angstrom.ucdavis.edu/</a><br>