Thank you very much , Prof Marzari .<br>Why can we safely treat metallic nanotubes with wfs' centers change ? <br>Just because of its feature DOS pattern at Fermi level ？<br><br>With Regards，<br>Hai-Ping<br><br><br><div>
<span class="gmail_quote">On 9/19/07, <b class="gmail_sendername">Nicola Marzari</b> <<a href="mailto:marzari@mit.edu">marzari@mit.edu</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
lan haiping wrote:<br>> Dear Stefano,<br>> i notice such problem, but in Prof Marzari's work on cnt, the transverse<br>> polarizabilities of metallic nanotubes are given. My confusion may be<br>> due to this example.
<br>> Thank you<br>><br>> Regards<br>> Hai-Ping<br><br><br>Dear Hai-Ping,<br><br>1) the transverse polarizabilities are finite for both metallic<br>and insulating nanotubes. It's the longitudinal one that is
<br>infinite in metallic tubes. Note that 3n,0 tubes at small diameters<br>are semiconducting with small gaps.<br><br>2) as mentioned, we did calculate them in real space from the integral<br>of the charge density. This is an appropriate operation for a finite,
<br>isolated system - in the transverse direction this is what they are.<br><br>3) re. electric enthalpy - not sure what the status of that is.<br>I'll try to discuss it when Paolo Umari visits later in October.<br><br>
4) you could use WFs - both for truly semiconducting nanotubes,<br>and even for the worse case scenario of (n,n) armchair (metallic)<br>ones. Treat the system as insulating, and you should<br>find a solution with WFs that corresponds to covalent bonds,
<br>and 1 p_z-like WF every 2 carbons. The center displacement as a<br>function of field gives you the polarizaton.<br><br>Best,<br><br> nicola<br><br><br>---------------------------------------------------------------------
<br>Prof Nicola Marzari Department of Materials Science and Engineering<br>13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA<br>tel 617.4522758 fax 2586534 <a href="mailto:marzari@mit.edu">marzari@mit.edu
</a> <a href="http://quasiamore.mit.edu">http://quasiamore.mit.edu</a><br>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum">
http://www.democritos.it/mailman/listinfo/pw_forum</a><br></blockquote></div><br><br clear="all"><br>-- <br>Hai-Ping Lan <br>Department of Electronics ,<br>Peking University , Bejing, 100871<br><a href="mailto:lanhaiping@gmail.com">
lanhaiping@gmail.com</a>, <a href="mailto:hplan@pku.edu.cn">hplan@pku.edu.cn</a>