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<div class="moz-cite-prefix">Dear Sapna Bondwal,<br>
<br>
pw.x (almost**) always describes systems that are periodic so if
you desire to approximately describe an isolated cluster you need
to surround it by some vacuum space so that periodically repeated
images interact as little as possible.<br>
<br>
let's say you want to describe SiH4, let's say SiH bondlength is
about 1.5 AA, so the molecule is about spherical with a diameter
twice as much, 3 AA... add 6-7 AA of vacuum to separate it from
its periodic image and you get ~20 a.u.: a SC cell of that size
should be reasonable.<br>
<br>
the easiest way to specify the coordinates is to choose
ATOMIC_POSITIONS in angstrom or bohr so you don't have to bother
about rescaling them when you test convergence w.r.t. cell size...
something that you should always do to make sure your cluster is
really isolated.<br>
<br>
**Once you are at ease with this simple calculations for isolated
molecules you can explore the<br>
effect of the assume_isolated flag (there are various options that
correct for the spurious interactions among periodical images with
various degrees of sophistication)<br>
<br>
stefano<br>
<br>
<br>
On 11/10/2015 14:30, sapna bondwal wrote:<br>
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cite="mid:CAK3mcGhUyWug+kmbSr0+ttNFgmoLQ1+LmzuyCT9izKngCnb5JA@mail.gmail.com"
type="cite">
<div dir="ltr">Hello,
<div><br>
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<div>I am working on Silicon nanoclusters. A nanocluster is not
a periodic, so one needs to create artificial periodicity
using supercell. I choose say, ibrave = 1 i.e cubic lattice,
cell dimensions= 20.00. Could someone guide me how to create a
supercell using these parameters? How to give coordinated of a
cluster for example Si5 or SiH4? How to specify the vacuum
space, Cell length? Could someone give me clear idea about my
query? What is the importance of supercell approach? I request
someone to give a simple illustartion so that I am able to
appreciate the supercell approach in a better way.</div>
<div><br>
</div>
<div>Thank You in advance.<br clear="all">
<div><br>
</div>
-- <br>
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<div><br>
</div>
Sapna Bondwal
<div>Research Scholar</div>
<div>Theoretical Chemistry Lab</div>
<div>IIT ROORKEE<br>
<div><br>
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