<div dir="ltr">Dear Hongsheng,<div><br></div><div>I don't understand why I should use relax instead of vc-relax. As far as I understand, when a system is under pressure, both the atomic positions inside a unit cell, as well as the dimensions of the unit cell changes. So, why should I keep the unit cell parameters fixed if I am interested in finding phase transitions?</div>
<div><br></div><div>Thanks<br><br><div class="gmail_quote">On Mon, Jul 18, 2011 at 4:04 AM, Hongsheng Zhao <span dir="ltr"><<a href="mailto:zhaohscas@yahoo.com.cn">zhaohscas@yahoo.com.cn</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="im">On 07/18/2011 09:40 AM, Amin Torabi wrote:<br>
> Dear experts!<br>
><br>
> Forgive me for my naive question... but I am interested in<br>
> pressure-induced phase transitions of diborane. Could you please have a<br>
> look at my input file, attached to this message.<br>
><br>
> The following is what I think I should do: (correct me if I'm wrong!)<br>
><br>
> 1. doing separate vc-relax calculation at each pressure<br>
<br>
</div>By using this method, there are some limitations. You should have known<br>
in advance the different phases between them the phase transition maybe<br>
occur when we change the pressure. Then you can use this method to<br>
determine the phase transition path. But I'm not so sure this method<br>
can predict all of the possible phases for a system when we change the<br>
external pressure. To do a more reasonable and complete phase<br>
transition prediction and even searching for unknown phases, you should<br>
use some third-party code like uspex for this type of job.<br>
<br>
In addition, I think you should do relax, not vc-relax calculation at<br>
each pressure. If you do vc-relax, then the pressure imposed to the<br>
system will be released. So you won't get the *Pressure-induced* phase<br>
transition.<br>
<div class="im"><br>
> 2. comparing the optimized cell_parameters at each pressure to see when<br>
> the structure changes<br>
><br>
> I am wondering how I can use the enthalpy or unit cell volume at each<br>
> pressure to make sure that a phase transition has occurred<br>
<br>
</div>For the other questions, see this thread on this list: About the method<br>
to obtain the common tangent for determing the phase transition<br>
pressure. HTH.<br>
<br>
Regards<br>
<div class="im">><br>
> Thanks in advance<br>
><br>
><br>
> --<br>
> Amin Torabi<br>
> Ph.D. Student<br>
> Chemistry Department<br>
> /The/ University /of/ Western Ontario<br>
> London, On Canada, N6A 5B7<br>
> Phone: <a href="tel:519-661-2111%20Ext%3A%2087871" value="+15196612111">519-661-2111 Ext: 87871</a><br>
> ****************************************<br>
><br>
><br>
><br>
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<br>
--<br>
Hongsheng Zhao <<a href="mailto:zhaohscas@yahoo.com.cn">zhaohscas@yahoo.com.cn</a>><br>
School of Physics and Electrical Information Science,<br>
Ningxia University, Yinchuan 750021, China<br>
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</font></blockquote></div><br><br clear="all"><br>-- <br><div dir="ltr">Amin Torabi<br>Ph.D. Student<br>Chemistry Department<br><i>The</i> University <i>of</i> Western Ontario<br>London, On Canada, N6A 5B7<br><span style="font-family:'Droid Sans', arial, sans-serif;font-size:13px;border-collapse:collapse;color:rgb(32, 32, 32)">Phone: <a value="+15196612111" style="color:rgb(103, 117, 58)">519-661-2111</a> Ext: 87871</span><div>
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