[Pw_forum] how to convert to unit of eV/atom in supercell?

[Duy Le]

Perhaps Kenvin refers to cohesive energy.

If you know exactly what you want to calculate, you will be able to
calculate.  So please make sure you understand the quantity.
--------------------------------------------------
Duy Le
PhD Student
Department of Physics
University of Central Florida.

"Men don't need hand to do things"



On Thu, Feb 4, 2010 at 8:53 AM, Gabriele Sclauzero <sclauzer at sissa.it> wrote:
> Dear Kelvin,
>
>   please make a serious effort to include in your responses only relevant emails:
> replying to digests is quite not a good idea... I had to scroll hundreds of lines before
> getting to the right point.
>
>
>>     Message: 4
>>     Date: Thu, 04 Feb 2010 09:08:41 +0100
>>     From: Gabriele Sclauzero <sclauzer at sissa.it <mailto:sclauzer at sissa.it>>
>>     Subject: Re: [Pw_forum] how to conver to unit of eV/atom in supercell?
>>     To: PWSCF Forum <pw_forum at pwscf.org <mailto:pw_forum at pwscf.org>>
>>     Message-ID: <4B6A8089.9080009 at sissa.it
>>     <mailto:4B6A8089.9080009 at sissa.it>>
>>     Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>>
>>
>>     Wong Kelvin wrote:
>>      > Dear all
>>      >
>>      > when i calculate a single atomc Cu primitive cell, the energy is
>>     ~ -87
>>
>>     What are you trying to compute? An isolated atom or a bulk phase? In
>>     any case, if you are
>>     using pseudopotentials the total energy has not any physical meaning
>>     by itself. What is
>>     physically relevant are energy differences.
>>
>>      > Ry. How to convert it to the eV/atom which normally is around
>>     -3.7 eV?
>>
>>     Where did you get this value of -3.7 and what does it actually refer
>>     to? I mean, to which
>>     physical quantity?
>>
>>
>>     GS
>>      > Thanks
>>      > Wong
>>      >
>>      >
>>     o ------------------------------------------------ o
>>     | Gabriele Sclauzero, PhD Student                  |
>>     | c/o:   SISSA & CNR-INFM Democritos,              |
>>     |        via Beirut 2-4, 34014 Trieste (Italy)     |
>>     | email: sclauzer at sissa.it <mailto:sclauzer at sissa.it>
>>               |
>>     | phone: +39 040 3787 511                          |
>>     | skype: gurlonotturno                             |
>>     o ------------------------------------------------ o
>>
>> Dear Gabriele
>> Thanks for reply!
>>
>> I am trying to calculate the grain and twin boundary energies in metals.
>
> I don't think that any code can give this energies with a single total energy calculation.
> You have first to learn the general methodology to build these quantities.
>
>> I partially understand that absolute energy in pseudopotential
>> calculation does not provide meaningful interpretation.
>
> If you are dealing with a bulk phase it's not only a matter of pseudopotential, since you
> are considering an infinitely extended solid.
> On the other hand, all electron energies of an isolated atom, if studied in a large enough
> supercell, I think they would have a physical meaning.
>
>> The reported energies in literature for copper with PP calculations use
>> to be around -3.7 eV/atom. Is there anything significant abt this
>> figure? and i do not understand how to get it. simple by diving the
>> total energy calculated by number of atom in supercell? if it is so, the
>
> Although I never did such kind of calculations, I don't believe that it's so simple to get
> that number. You should learn this from some textbook or lecture notes, rather than from
> this forum (which should treat more technical issues). Maybe if you are lucky some user
> with more experience on this will give you advice.
>
>
> GS
>
>> value (~3.7) is way too small as compare to the 87 Ry for one copper
>> atom primitive cell.
>>
>> regards
>> Kelvin
>>
>
> --
>
>
> o ------------------------------------------------ o
> | Gabriele Sclauzero, PhD Student                  |
> | c/o:   SISSA & CNR-INFM Democritos,              |
> |        via Beirut 2-4, 34014 Trieste (Italy)     |
> | email: sclauzer at sissa.it                         |
> | phone: +39 040 3787 511                          |
> | skype: gurlonotturno                             |
> o ------------------------------------------------ o
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>