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<div class="moz-cite-prefix">is your system a free-standing thin
film or aims at representing a surface ?<br>
<br>
in the former case you need to relax (only in the xy plane), in
the latter the in-plane lattice parameters should be fixed to the
(theoretical)bulk values of your system.<br>
<br>
stefano<br>
<br>
<br>
On 11/12/2015 09:33, Jaret Qi wrote:<br>
</div>
<blockquote
cite="mid:1394274522.604943.1449822794459.JavaMail.yahoo@mail.yahoo.com"
type="cite">
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font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial,
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<div id="yui_3_16_0_1_1449820684210_6674">Hello QE users,</div>
<div id="yui_3_16_0_1_1449820684210_6674" dir="ltr">I need to
add vacuum along the z-direction to study E-field effect using
saw-like potential. In this case do I need to do vc-relax or
relax will be enough?</div>
<div id="yui_3_16_0_1_1449820684210_6674" dir="ltr"><br>
</div>
<div id="yui_3_16_0_1_1449820684210_6674" dir="ltr">Thank you in
advance,</div>
<div id="yui_3_16_0_1_1449820684210_6674" dir="ltr">Jaret</div>
<div id="yui_3_16_0_1_1449820684210_6674" dir="ltr">ASU</div>
</div>
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