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<DIV><FONT face=Arial size=2>It means that you have to perform calculations for
pure Si and pure C in the same structure. These values can not be derivated from
the same calculations of the compound.</FONT></DIV>
<DIV><FONT face=Arial size=2>Then, for your SiC compound with 50at%C, you have
Eformation = Total E (SiC) - .5 Total E(Si) - .5 Total E(C)
</FONT></DIV>
<DIV><FONT face=Arial size=2>This is what you usually find in literature (for
example C Colinet and A Pasturel, J Phase Equilibria vol 15 No 3
(1994)).</FONT></DIV>
<DIV><FONT face=Arial size=2>Paula.</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=rcais@cal3.vsnl.net.in
href="mailto:rcais@cal3.vsnl.net.in">Chandrika</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=wien@zeus.theochem.tuwien.ac.at
href="mailto:wien@zeus.theochem.tuwien.ac.at">A Mailing list for WIEN2k
users</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, September 27, 2005 1:58
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Wien] total energy value
too high</DIV>
<DIV><FONT face=Arial size=2></FONT><FONT face=Arial size=2></FONT><BR></DIV>
<DIV><FONT face=Arial size=2>Dear Paula,</FONT></DIV>
<DIV><FONT face=Arial size=2>Many thanks for the suggestion.</FONT></DIV>
<DIV><FONT face=Arial size=2>Does this mean that I should do total energy
derivations for (i) a structure containing only Si (ii) a structure containing
only C and (iii) subtract from the total energy for SiC. </FONT></DIV>
<DIV><FONT face=Arial size=2>Or are these values available within the
derivations for SiC itself?</FONT></DIV>
<DIV><FONT face=Arial size=2>Thank you,</FONT></DIV>
<DIV><FONT face=Arial size=2>Chandrika</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=pralonso@cnea.gov.ar href="mailto:pralonso@cnea.gov.ar">Paula R.
Alonso</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=wien@zeus.theochem.tuwien.ac.at
href="mailto:wien@zeus.theochem.tuwien.ac.at">A Mailing list for WIEN2k
users</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, September 26, 2005 9:07
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: [Wien] total energy value
too high</DIV>
<DIV><FONT face=Arial size=2></FONT><BR></DIV>
<DIV>
<DIV><FONT face=Arial size=2>Free energy </FONT><FONT face=Arial
size=2>of formation is referred to the pure structures. You have to substrat
from the total energy of the compound the total energy of the pure elements
in the same structure, weighted by atomic fraction.</FONT></DIV>
<DIV><FONT face=Arial size=2>You obtain total energy in Ry/cell. You
must first convert it to Ry/at. T</FONT><FONT face=Arial size=2>hen, 1Ry/at
</FONT><FONT face=Arial size=2>= 13.13 x 10^5 Joule/
mole .</FONT></DIV>
<DIV><FONT face=Arial size=2>Paula Alonso</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV>Departamento de Materiales – Centro Atómico Constituyentes</DIV>
<DIV>Comisión Nacional de Energía Atómica</DIV>
<DIV>Avda Gral Paz 1499, San Martín, Buenos Aires, CP B1650KNA</DIV>
<DIV> Argentina.</DIV>
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<DIV style="FONT: 10pt arial">----- Original Message -----
</DIV></BLOCKQUOTE></DIV>
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<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=rcais@cal3.vsnl.net.in
href="mailto:rcais@cal3.vsnl.net.in">Chandrika</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=Wien@zeus.theochem.tuwien.ac.at
href="mailto:Wien@zeus.theochem.tuwien.ac.at">Wien@zeus.theochem.tuwien.ac.at</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, September 26, 2005 3:40
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Wien] total energy value
too high</DIV>
<DIV><FONT face=Arial size=2></FONT><FONT face=Arial
size=2></FONT><BR></DIV>
<DIV><FONT face=Arial size=2>Hello Wien Users,</FONT></DIV>
<DIV><FONT face=Arial size=2>I am trying to derive the total energy of SiC
in order to later derive its standard free energy of formation. With all
three options in Wien2k 05 (13, 14 and 5) I get values near -656 Ry.
</FONT><FONT face=Arial size=2>(i) I presumed that the value derived by
Wien is Ry <EM>per unit cell</EM>. Is that correct?</FONT></DIV>
<DIV><FONT face=Arial size=2>(i) Therefore to convert to kcal/mole, I
used 1Ry = 13.13 x 10^5 Joule/ mole . Is this okay?</FONT></DIV>
<DIV><FONT face=Arial size=2>(iii) The derived value of total energy of
SiC is then -861300 KJoule/mole. This is several orders of magnitude
higher than the free energy of formation of SiC which is -72.2
KJoule/mole.</FONT></DIV>
<DIV><FONT face=Arial size=2>Could anyone suggest where I have gone
wrong?</FONT></DIV>
<DIV><FONT face=Arial size=2>I would particularly like to know about the
conversion units.</FONT></DIV>
<DIV><FONT face=Arial size=2>Thanks in advance.</FONT></DIV>
<DIV><FONT face=Arial size=2>Chandrika</FONT></DIV>
<DIV><FONT face=Arial
size=2>-----------------------------------------------------------------------------------------<BR>Dr
(Ms) Chandrika Varadachari<BR>Raman Centre for Applied and
Interdisciplinary Sciences<BR>16A Jheel Road<BR>Calcutta
700075<BR>India<BR>Tel : 91-33-24830029<BR>Fax : 91-33-24180610<BR>web :
<A href="http://www.rcais.org.in">www.rcais.org.in</A></FONT></DIV>
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