<div> </div>
<div>Thanks, Paolo. I have little confusion about your comment though. </div>
<div> </div>
<div>Earlier I had used norm-conserving PP in supercell calculations as well; that produced converged frequency of 518.2 for Si. So, is it possible that linear response calculations might not give better results compared to supercell calculations (which is very expensive). The result could be sensitive to the assumptions of linear response theory as well?? </div>
<div> </div>
<div>Thanks, </div>
<div>Sophia </div>
<div><br> </div>
<div class="gmail_quote">On Mon, May 25, 2009 at 1:26 AM, Paolo Giannozzi <span dir="ltr"><<a href="mailto:giannozz@democritos.it">giannozz@democritos.it</a>></span> wrote:<br>
<blockquote style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote">
<div class="im"><br>On May 24, 2009, at 23:04 , Sophia Nishad wrote:<br><br>> it is still off from the experiemntal value by ~8cm-1.<br><br></div>both pseudopotentials and approximations to the exchange-correlation<br>
functional introduce intrinsic errors. It is quite hard to get any<br>better<br>results than those you get.<br><br>Paolo<br>---<br>Paolo Giannozzi, Democritos and University of Udine, Italy<br><br><br>_______________________________________________<br>
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<div></div><br>-- <br>Sophia<br>