[Pw_forum] Pw_forum Digest, Vol 24, Issue 55

[ambavale sagar]

Dear Sir,
Thank you very much for your kind guidance. I will do the exercise.

best regards
Sagar




________________________________
Message: 6
Date: Thu, 25 Jun 2009 07:40:12 -0400
From: Nicola Marzari <marzari at MIT.EDU>
Subject: Re: [Pw_forum] energy origin in espresso
To: PWSCF Forum <pw_forum at pwscf.org>
Message-ID: <4A43621C.8030509 at mit..edu>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Paolo Giannozzi wrote:

>> then one have to use a common reference to compare
>> the levels of different calculations. For this purpose one
>> can use e.g. take a hydrogen molecule 10 ? away from
>> the slab or molecule, whose bonding orbital can be taken
>> as reference.
> 
> yes, this is a simple way to find a common alignment


Dear Ambavale,


to elaborate on Paolo's comment: this is one of the two common
ways to do it. The other would be to do a plot of the electrostatic
potential - far away form the slab it will become flat (unless your
slab, e.g., has a surface dipole - then you'll learn you have
a small problem, and need to be careful about electrostatic
interactions between different charges).

But suppose it will become flat - that will point to the reference
zero energy of that calculation. You redo this for all calculations,
and you have reference points of each of them.

Use this approach, and the one where you add the hydrogen molecule.
Do they give you the same results ? In principle they should - if they
do not, you need to figure out what is the problem, and in the process 
you learn a lot about accuracy.

Warmly recommended,

            nicola

-- 
---------------------------------------------------------------------
Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu


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End of Pw_forum Digest, Vol 24, Issue 55
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