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<DIV><FONT face=Arial size=2>Dear Paula & Stefaan,</FONT></DIV>
<DIV><FONT face=Arial size=2>I tried as you had suggested but the value derived
is several orders of magnitude too high.</FONT></DIV>
<DIV><FONT face=Arial size=2>Should the derivation rather be :</FONT></DIV>
<DIV><FONT face=Arial size=2>Eformation = Total E (SiC) - Total
E(Si) - Total E(C) </FONT></DIV>
<DIV><FONT face=Arial size=2>because one unit cell of SiC has one atom of Si and
one atom of C.</FONT></DIV>
<DIV><FONT face=Arial size=2>In this case I derive value for a unit cell which I
then convert to one mole by multiplying by the Avogadro number (N).</FONT></DIV>
<DIV><FONT face=Arial size=2>I ultimately need to derive gibbs free energy of
formation (standard free energy of formation).</FONT></DIV>
<DIV><FONT face=Arial size=2>Which quantity should I be looking at?</FONT></DIV>
<DIV><FONT face=Arial size=2>I would appreciate your suggestions once
more.</FONT></DIV>
<DIV><FONT face=Arial size=2>Thank you very much in advance.</FONT></DIV>
<DIV><FONT face=Arial size=2>Chandrika</FONT></DIV>
<DIV>-----------------------------------------------------------------------------------------<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></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> Tuesday, September 27, 2005 7:19
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: [Wien] total energy value
too high</DIV>
<DIV><BR></DIV>
<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 -----
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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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