[Pw_forum] How to compute surface energy and adsorbed energy ?

[Stefano Baroni]

On Jul 3, 2008, at 4:45 AM, wangqj1 wrote:

>  Dear pwscf users;

Dear Mr. Unknown

>  Could someone tell me 'how to compute surface energy and adsorbed  
> energy '?

I am afraid, this question would be more appropriate for your  
supervisor than for this forum.

in any event, think of the definition of surface energy:
"surface energy" = energy necessary to cut an infinite solid into two  
semi-infinite parts (or in many slabs, for that matter, provided you  
count properly the number of slabs). right? now you can calculate the  
energy of bulk system (the result is infiite: what you get is an  
energy per unit volume, or an energy per atom). you can also calculate  
the energy of a system made of many (infinite, because of periodic  
boundary conditions) slabs. The enrgy per atom will be different. the  
difference will be proprortional to the surface area ... can you see  
now how the calculation would proceed?

The same would apply to "adsorption" (NOT "adsorbed") energy = energy  
of a surface (or a slam, for that matter) with an adsorbed molecule,  
minus the sum of energy of an isolated (clean) surface and of an  
isolated molecule.

>  whether the surface energy is the whole energy or not ?

do not undesrtand what you mean. think of the definitiion above

>  I am looking forward to your advice .
> Thanks!

would be so kind as to provide your name and full affiliation, the  
next time you write to this forum?

Thanks - SB

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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

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