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<p>Dear <font style="font-size:11pt" color="#000000" face="Calibri, sans-serif">Mian Fayyaz Ahmad</font>,</p>
<p> BiFeO3 is a complex compound with many crystalline structures.</p>
<p> If you have a triclinic structure then you need to optimize 'a', 'b', 'c', 'alpha', 'beta' and 'gamma'. But you have to optimize the internal coordinates.</p>
<p><br>
</p>
<p> I will exemplify with a tetrahedral structure; you have a=b, c, angles=90.</p>
<p> The WIEN2k now does in one cycle, but 10 years ago was not the case. </p>
<p><br>
</p>
<p> Those days you would change the 'c' parameter by -6%, -3%, 0%, 3% and 6%, then after optimizing these 5 cases you would adjust a cubic curve, now it is a Murnaham curve, and find the minimum for 'c'.</p>
<p> Then you would optimize 'a' (=b)</p>
<p> And the last part of the first cycle would be an optimization of the internal coordinates;</p>
<p><br>
</p>
<p> min -j "run -ec 0.0001 -fc 5"</p>
<p><br>
</p>
<p> '-fc' is force convergence, and I find 5 to be good, even stronger than '-ec 0.0001'</p>
<p> Careful, if you do not put '-ec' it can happen that the force is optimized but the energy not, then you have problems.<br>
</p>
<p><br>
</p>
<p> Then you would return to the optimize the 'c' parameter and continue until the parameters change little.</p>
<p><br>
</p>
<p> For the case of a triclinic system then you have in each cycle to optimize (1) 'a', (2) 'b', (3) 'c', (4) 'alpha', (5) 'beta' and (6) 'gamma' and at the end (7) internal coordinates.</p>
<p><br>
</p>
<p> So it is a long process.</p>
<p><br>
</p>
<p> Now, the 'a', 'b' and 'c' parameters can be optimized in one step as you can see in the new WIEN2k. In this case you can choose a 3x3x3 or 4x4x4 or 5x5x5 mesh.<br>
</p>
<p> The same could be done for 'alpha', 'beta' and 'gamma', but you need to find the nxnxn mesh yourself.</p>
<p><br>
</p>
<p> I hope that this gives you a general guide.</p>
<p><br>
</p>
<p> Saludos</p>
<p><br>
</p>
<p> Pablo de la Mora<br>
</p>
<p></p>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" color="#000000" face="Calibri, sans-serif"><b>De:</b> wien-bounces@zeus.theochem.tuwien.ac.at <wien-bounces@zeus.theochem.tuwien.ac.at> en nombre de Mian Fayyaz Ahmad <fayyaz.pc@gmail.com><br>
<b>Enviado:</b> lunes, 23 de junio de 2014 10:51 p.m.<br>
<b>Para:</b> A Mailing list for WIEN2k users<br>
<b>Asunto:</b> Re: [Wien] Formula to calculate Lattice Constant and angle of BiFeO3</font>
<div> </div>
</div>
<div>
<div dir="ltr">Respected, "<span style="color:rgb(85,85,85); font-family:arial,sans-serif; font-size:13px; white-space:nowrap"><a href="mailto:delamora@unam.mx">delamora@unam.mx</a>"</span>
<div><span style="color:rgb(85,85,85); font-family:arial,sans-serif; font-size:13px; white-space:nowrap"> Still i am confusing how to calculate . As you mentioned but still confusion about concrete steps as you mentioned </span></div>
<div><span style="color:rgb(85,85,85); font-family:arial,sans-serif; font-size:13px; white-space:nowrap">( </span><span style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px">First you optimize a, b, c</span></div>
<div><span style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px">then you vary alpha and optimize, then beta and finally gamma</span></div>
<p style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px; margin-top:0px; margin-bottom:0px">
then you return to the beginning;<br>
</p>
<p style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px; margin-top:0px; margin-bottom:0px">
optimize a, b and c</p>
<p style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px; margin-top:0px; margin-bottom:0px">
until the changes in the cell parameters change little.).</p>
<p style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px; margin-top:0px; margin-bottom:0px">
According to user guide at page #66 (listed from 1-6 ) in volume optimization case.<br>
</p>
<p style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px; margin-top:0px; margin-bottom:0px">
Please guide me according to list in user guide step wise. </p>
<p style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:16px; margin-top:0px; margin-bottom:0px">
I would be very thankful to you.</p>
<div><br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Jun 24, 2014 at 12:30 AM, delamora <span dir="ltr">
<<a href="mailto:delamora@unam.mx" target="_blank">delamora@unam.mx</a>></span> wrote:<br>
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<p>Yes, in the WIEN2k you find a, b and c optimization all set for you, but ti include the angles the number of structures would increase exponentially;</p>
<p>1 dimension n</p>
<p>2 dimensions n**2</p>
<p>3 dimensions n**3</p>
<p>4 dimensions n**4</p>
<p>5 dimensions n**5</p>
<p>6 dimensions n**6</p>
<p><br>
</p>
<p>4**6=4096</p>
<p><br>
</p>
<p>So you must do each optimization separately</p>
<p>First you optimize a, b, c</p>
<p>then you vary alpha and optimize, then beta and finally gamma</p>
<p><br>
</p>
<p>then you return to the beginning;<br>
</p>
<p>optimize a, b and c</p>
<p>until the changes in the cell parameters change little.<br>
</p>
<p><br>
</p>
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<div dir="ltr"><font style="font-size:11pt" color="#000000" face="Calibri, sans-serif"><b>De:</b>
<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a> <<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a>> en nombre de Mian Fayyaz
Ahmad <<a href="mailto:fayyaz.pc@gmail.com" target="_blank">fayyaz.pc@gmail.com</a>><br>
<b>Enviado:</b> domingo, 22 de junio de 2014 09:41 p.m.<br>
<b>Para:</b> <a href="mailto:Wien@zeus.theochem.tuwien.ac.at" target="_blank">Wien@zeus.theochem.tuwien.ac.at</a><br>
<b>Asunto:</b> [Wien] Formula to calculate Lattice Constant and angle of BiFeO3</font>
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<div><i><b><font style="background-color:rgb(255,255,255)" color="#0000ff" face="comic sans ms, sans-serif">Respected, Wien2K Community</font></b></i></div>
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<div><i><b><font style="background-color:rgb(255,255,255)" color="#0000ff" face="comic sans ms, sans-serif"> I want to </font></b></i><font color="#0000ff" face="comic sans ms, sans-serif"><b><i>calculate Lattice Constant and angle of BiFeO3 in space group
P1( Triclinic ). I have done volume optimization. I found a formula [V = abc( 1−cos**2alpha −</i></b></font><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>cos**2beta</i></b><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>− </i></b><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>cos**2gamma</i></b><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>+2*</i></b><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>cos
alpha*</i></b><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>cos beta*</i></b><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>cos gamma)**1/2]. I found only volume in volume optimization. How can i found lattice
parameters a, b , c and angles??? </i></b></div>
<div><b style="color:rgb(0,0,255); font-family:"comic sans ms",sans-serif"><i>please help me in this regard.</i></b><br>
</div>
<div><font color="#0000ff" face="comic sans ms, sans-serif"><b><i>thanks in advance</i></b></font></div>
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