Thanks for you reply. My minimization stops with a message saying that the force is minimized and the force and energy are inconsistent. So I carried out another calculation by using the structure file that I got. However, the force on one of the atoms is as large as 26. Is it too large to be used as a equilibrium state?<div>
Thanks a lot.</div><div><br></div><div>Yundi<br><br><div class="gmail_quote">2011/8/31 å×ÇÅÎÉÑ ëÁÂÌÉÍÁÎ <span dir="ltr"><<a href="mailto:evgeniya@theochem.tuwien.ac.at" target="_blank">evgeniya@theochem.tuwien.ac.at</a>></span><br>
<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex">I mean minimization of internal parameters (lattice coordinates) in your initial structure. This is a crucial point. You should not have forces on atoms, since it is a kind of reference state. The structure optimization (lattice parameters) itself is less crucial as long as you have the reasonable lattice parameters.<br>
<br>Once you have a well relaxed structure, you can construct atomic displacements and calculate 'total forces' using force convergence criteria (-fc) at fixed lattice constants. <br><br>Total forces, which you need for phonon calculations, are the derivatives of total energies with respect to atomic displacements. Therefore, in order to get more precise values of total forces one usually constructs big supercells. This means that a size of your supercell is also important.</blockquote>
<div>š</div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex"><div><div></div><div><br>
š<br><br><div class="gmail_quote">2011/8/31 Yundi Quan <span dir="ltr"><<a href="mailto:quanyundi@gmail.com" target="_blank">quanyundi@gmail.com</a>></span><br><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex">
By relaxing structure, do you mean internal structure or the crystal structure or both?<br><font color="#888888"><br>Yundi</font><div><div></div><div><br><br><div class="gmail_quote">2011/8/31 å×ÇÅÎÉÑ ëÁÂÌÉÍÁÎ <span dir="ltr"><<a href="mailto:evgeniya@theochem.tuwien.ac.at" target="_blank">evgeniya@theochem.tuwien.ac.at</a>></span><br>
<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex">Fisrt you have to relax your structure until you have no forces on all your atoms. Then you create the displacements and perform scf calculations without minimization.<br>
<br><div class="gmail_quote"><div>2011/8/31 Yundi Quan <span dir="ltr"><<a href="mailto:quanyundi@gmail.com" target="_blank">quanyundi@gmail.com</a>></span><br>
</div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex"><div>Hi, When doing phonon calculation, do I have to do structure minimization first?<div>
<br></div><font color="#888888"><div>
Yundi</div>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Evgeniya Kabliman.<br>Insitute of Materials Chemistryš š š šš Vienna University of Technology<br>Getreidemarkt 9/165-TC, A-1060 Vienna, Austria<br>Tel: <a href="tel:%2B43%201%2058801%2015674" value="+4315880115674" target="_blank">+43 1 58801 15674</a>š š š š Fax: <a href="tel:%2B43%201%2058801%2015698" value="+4315880115698" target="_blank">+43 1 58801 15698</a><br>
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