sir <div>i am using quantum espresso 4.3 version</div><div>i want to study the phase transition of yitrium nitride(yn)</div><div>first by doing scf calculation at 0k </div><div>i found a phase transition of B1 to B2 transition at 137 gpa for this i used a 14*14*14 kpoints mesh and convergence achived for scf is 10^-9 </div>
<div>i used GGA psudo potentials of pbe type avalable in code of espresso website for y and n</div><div>but when i did the calculation for phonon dispersion </div><div>B2 stucter instablity (negative frequency ) in phonon spectrum continues upto 500 gpa why ?</div>
<div>for this i used 4*4*4* mesh q points for dyanamical matrices i have incresed further but nothing results</div><div><br><div class="gmail_quote">On Sat, May 28, 2011 at 9:36 PM, Stefano de Gironcoli <span dir="ltr"><<a href="mailto:degironc@sissa.it">degironc@sissa.it</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div bgcolor="#ffffff" text="#000000">
Dear Bhabya Sahoo,<br>
<br>
your very stingy use of punctuation make quite difficult (at
least for me) to follow your request...<br>
Take your time and try to make you clear providing more detailed
information about your system, what is your aim, what is the
problem, what are the tests you have done.<br>
No one is going to spend more time in thinking about your problem
than you do in explaining it.<br>
<br>
Please provide your affiliation.<br>
<br>
stefano <br>
-<br>
Stefano de Gironcoli, SISSA and DEMOCRITOS<div><div></div><div class="h5"><br>
<br>
On 05/28/2011 05:46 PM, bhabya sahoo wrote:
</div></div><blockquote type="cite"><div><div></div><div class="h5">
<pre>i am using quantum espresso static calculation obeys thermdyanamic stability
transition from B1 to B2 transition at 138 gpa so ihave used 24 24 24
kpoint grid for phonon in B2 phase is calculated 4 4 4 grid by linear
response calculation but why the instability (negative frequency in phonon )
upto 450 gpa i have used pbe psudo potentials also the lattice constant is
exact for experimental data
can metastability have negative frequency so why this occures
optimisation is ok
other problem why free energy is not coming for unstable phase for qha code
in quantum espresso
replay immidiate if u have solution
On Sat, May 28, 2011 at 5:38 PM, bhabya sahoo <a href="mailto:bdslipun@gmail.com" target="_blank"><bdslipun@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre>sir
i used to calculate the phonon calculation on a 4*4*4 grid in cscl phase
but the unstability persists upto 500 gpa
but it is the thermodyanamic stability after 140 gpa kpoints 24*24*24
what may be reseon i donot know
please help me
</pre>
</blockquote>
<pre></pre>
</div></div><pre><fieldset></fieldset>
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