<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman,new york,times,serif;font-size:12pt"><div>Dear Sir,<br>Thank you very much for your kind guidance. I will do the exercise.<br><br>best regards<br>Sagar<br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;"><font size="2" face="Tahoma"><hr size="1"><b><span style="font-weight: bold;"></span></b></font>Message: 6<br>Date: Thu, 25 Jun 2009 07:40:12 -0400<br>From: Nicola Marzari <<a ymailto="mailto:marzari@MIT.EDU" href="mailto:marzari@MIT.EDU">marzari@MIT.EDU</a>><br>Subject: Re: [Pw_forum] energy origin in espresso<br>To: PWSCF Forum <<a ymailto="mailto:pw_forum@pwscf.org" href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>Message-ID: <<a ymailto="mailto:4A43621C.8030509@mit.edu"
href="mailto:4A43621C.8030509@mit.edu">4A43621C.8030509@mit.edu</a>><br>Content-Type: text/plain; charset=ISO-8859-1; format=flowed<br><br>Paolo Giannozzi wrote:<br><br>>> then one have to use a common reference to compare<br>>> the levels of different calculations. For this purpose one<br>>> can use e.g. take a hydrogen molecule 10 ? away from<br>>> the slab or molecule, whose bonding orbital can be taken<br>>> as reference.<br>> <br>> yes, this is a simple way to find a common alignment<br><br><br>Dear Ambavale,<br><br><br>to elaborate on Paolo's comment: this is one of the two common<br>ways to do it. The other would be to do a plot of the electrostatic<br>potential - far away form the slab it will become flat (unless your<br>slab, e.g., has a surface dipole - then you'll learn you have<br>a small problem, and need to be careful about electrostatic<br>interactions between different charges).<br><br>But suppose
it will become flat - that will point to the reference<br>zero energy of that calculation. You redo this for all calculations,<br>and you have reference points of each of them.<br><br>Use this approach, and the one where you add the hydrogen molecule.<br>Do they give you the same results ? In principle they should - if they<br>do not, you need to figure out what is the problem, and in the process <br>you learn a lot about accuracy.<br><br>Warmly recommended,<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 ymailto="mailto:marzari@mit.edu" href="mailto:marzari@mit.edu">marzari@mit.edu</a> <a href="http://quasiamore.mit.edu"
target="_blank">http://quasiamore.mit.edu</a><br><br><br>------------------------------<br><br>_______________________________________________<br>Pw_forum mailing list<br><a ymailto="mailto:Pw_forum@pwscf.org" href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br><br><br>End of Pw_forum Digest, Vol 24, Issue 55<br>****************************************<br></div></div></div><br>
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