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On 07/05/2010 11:54 AM, Padmaja Patnaik wrote:
<blockquote cite="mid:778140.61172.qm@web26106.mail.ukl.yahoo.com"
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valign="top">I am calculating for SiC. Below is the datas you have
asked for. <br>
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<br>
You are lucky since I'm also studying SiC right now. <br>
<br>
What is this supposed to be? Cubic 3C-SiC I guess? If so, I think that
your atomic structure is wrong. There are some C atoms in the wrong
place. If you look at it (with xcrysden, for instance), you will see
that some tetrahedra around the carbon are upwards down. I mean, the
should be all oriented in one direction.<br>
<br>
Please check again your structure.<br>
<br>
GS<br>
<br>
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&system<br>
ibrav=1, celldm(1) =16.4824, nat=64, ntyp=2,<br>
ecutwfc = 32.0,<br>
occupations='smearing', smearing='methfessel-paxton', degauss=0.02<br>
<br>
/<br>
&electrons<br>
mixing_beta = 0.7<br>
/<br>
ATOMIC_SPECIES<br>
Si 28.086 Si.pz-vbc.UPF<br>
C 12.00 C.pz-vbc.UPF<br>
ATOMIC_POSITIONS<br>
Si 0.000 0.000 0.000<br>
Si 0.250 0.250 0.000<br>
Si 0.250 -0.250 0.000<br>
Si -0.250 0.250 0.000<br>
Si -0.250 -0.250 0.000<br>
Si 0.250 0.000 0.250<br>
Si 0.250 0.000 -0.250<br>
Si -0.250 0.000 0.250<br>
Si -0.250 0.000 -0.250<br>
Si 0.000 0.250 0.250<br>
Si 0.000 0.250 -0.250<br>
Si 0.000 -0.250 0.250<br>
Si 0.000 -0.250 -0.250<br>
Si 0.500 0.000 0.000<br>
Si 0.000 0.500 0.000<br>
Si 0.000 0.000 0.500<br>
Si 0.500 0.250 0.250<br>
Si 0.500 0.250 -0.250<br>
Si 0.500 -0.250 0.250<br>
Si 0.500 -0.250 -0.250<br>
Si 0.250 0.500 0.250<br>
Si 0.250 0.500 -0.250<br>
Si -0.250 0.500 0.250<br>
Si -0.250 0.500 -0.250<br>
Si 0.250 0.250 0.500<br>
Si 0.250 -0.250 0.500<br>
Si -0.250 0.250 0.500<br>
Si -0.250 -0.250 0.500<br>
Si 0.500 0.500 0.000<br>
Si 0.500 0.000 0.500<br>
Si 0.000 0.500 0.500<br>
Si 0.500 0.500 0.500<br>
C 0.125 0.125 0.125<br>
C -0.125 -0.125 0.125<br>
C 0.375 -0.125 0.125<br>
C -0.375 0.125 0.125<br>
C -0.125 0.375 0.125<br>
C 0.125 -0.375 0.125<br>
C 0.125 0.125 -0.375<br>
C -0.125 -0.125 -0.375<br>
C 0.375 0.375 0.125<br>
C -0.375 -0.375 0.125<br>
C 0.375 -0.125 -0.375<br>
C -0.375 0.125 -0.375<br>
C -0.125 0.375 -0.375<br>
C 0.125 -0.375 -0.375<br>
C 0.375 0.375 -0.375<br>
C -0.375 -0.375 -0.375<br>
C -0.125 0.125 0.125<br>
C 0.375 0.125 0.125<br>
C -0.125 -0.375 0.125<br>
C -0.125 0.125 -0.375<br>
C 0.375 -0.375 0.125<br>
C 0.375 0.125 -0.375<br>
C -0.125 -0.375 -0.375<br>
C 0.375 -0.375 -0.375<br>
C 0.125 -0.125 -0.125<br>
C -0.375 -0.125 -0.125<br>
C 0.125 0.375 -0.125<br>
C 0.125 -0.125 0.375<br>
C -0.375 0.375 -0.125<br>
C -0.375 -0.125 0.375<br>
C 0.125 0.375 0.375<br>
C -0.375 0.375 0.375<br>
K_POINTS {automatic}<br>
2 2 2 0 0 0<br>
<br>
I have repeated runs for different smearing, different k_points also.<br>
Sending you one of the input files.<br>
<br>
<br>
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Message: 1<br>
Date: Mon, 5 Jul 2010 10:34:54 +0200<br>
From: Gabriele Sclauzero <<a moz-do-not-send="true"
ymailto="mailto:sclauzer@sissa.it"
href="/mc/compose?to=sclauzer@sissa.it">sclauzer@sissa.it</a>><br>
Subject: Re: [Pw_forum] Problem in DOS results<br>
To: PWSCF Forum <<a moz-do-not-send="true"
ymailto="mailto:pw_forum@pwscf.org"
href="/mc/compose?to=pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>
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href="/mc/compose?to=FC6CD37D-AD91-4AC6-81A9-F89D070980A2@sissa.it">FC6CD37D-AD91-4AC6-81A9-F89D070980A2@sissa.it</a>><br>
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<br>
Dear Padmaja,<br>
<br>
are you sure that your calculation has been converged wrt the
k-point sampling? I believe that if you build the supercell correctly
and change the k-point sampling accordingly you'll get the same DOS. In
principle this should hold even if you didn't converge wrt the size of
the k-point mesh, though not completely sure that this is true also for
tetrahedra method occupations. <br>
<br>
Please post at least the atomic positions, lattice parameters and the
content of the K_POINTS input card, otherwise it will be impossible to
help you further...<br>
<br>
GS<br>
<br>
Il giorno 04/lug/2010, alle ore 21.56, Padmaja Patnaik ha scritto:<br>
<br>
> Dear all<br>
> <br>
> I am studying the properties of a compound semiconductor using
super cell calculations. I have generated super cells by expanding the
lattice constant 2times, 3 times and 4 times in all the directions. My
calculations gives correct results for 2 times and 4 times extended
super cells but not for 3 times extended onel. I have made sure that
the generated atomic co-ordinates are correct. I have tried fixing all
the required parameters like, k points, ecutwfc and nbnd. But still its
not working. after doing the scf calculations I do the DOS with
occupations=tetrahedra. But the DOS plot for the second case is found
to be much different from expected while for all other cases the
results match. What can be the probable mistake i am doing? Please
suggest.<br>
> <br>
> Padmaja Patnaik<br>
> Research Scholar<br>
> Dept of Physics<br>
> IIT Bombay<br>
> Mumbai, India<br>
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<pre class="moz-signature" cols="72">--
Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne
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