[Pw_forum] How to add air pressure on adsorption calculation using Pwscf

[Nicola Marzari]

Dear All,


in the low/ordinary pressure regime, one would use the chemical potential
(see Lorenzo's work, and e.g. the PRL circa 2005 by Reuter, Scheffler and
Frenkel). For high-pressure/condensed phase, you fix the number of 
molecules,
T and the volume - this last one either using the enthalpy that Oliviero
mentions, or just the free space in your supercell.

				nicola


On 28/10/2015 12:34, Oliviero Andreussi wrote:
> Well, as a matter of fact you could try to use the quantum-enthalpy
> functional of Matteo Cococcioni et al. Phys. Rev. Lett. *94*, 145501
>
> http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.94.145501
>
> Please double check that this is something that may be useful for your
> calculations. In case, the method is implemented in the CP code,
> PRESS_AI namelist, but also in PW by exploiting the external Environ
> module (which you would need to download and compile, more details can
> be found here www.quantum-environment.org). The actual release of
> Environ is compatible with QE 5.1, 5.1.1 and 5.1.2, if you are using a
> more recent version I could let you have the patch.
>
> Oliviero Andreussi
>
> Senior Postdoctoral Researcher
>
> École Polytechnique Fédérale de Lausanne (EPFL) and
>
> Università della Svizzera Italiana (USI) of Lugano
>
> Switzerland
>
>
>
>
> On 10/28/2015 10:05 AM, Lorenzo Paulatto wrote:
>> On Wednesday, October 28, 2015 04:13:41 PM 李睿 wrote:
>>> Hello, everyone
>>> I want to calculate molecules adsorption under 1Bar air pressure using
>>> Pwscf. Can I add air pressure in it?
>> No, you cannot. Gas pressure is a macroscopic variable. It does not exist in a
>> zero-temperature DFT calculation. You may do a molecular dynamics simulation
>> with a bunch of molecules at a certain temperature, but it is very impractical
>> and deducing the pressure from volume+temperature when the volume is so small
>> and includes a chemically reactive surface is not granted.
>>
>> What you can do is to include its effect via a chemical potential, you can
>> find a brief explanation in chapter 3.2 of my PhD thesis
>> <http://urania.sissa.it/xmlui/bitstream/handle/1963/5363/paulatto_thesis.pdf?sequence=1&isAllowed=y>
>> (eq. 3.12 in particular, but read all the chapter). If I remember correctly, I
>> studied the problem on  "Arthur W. Adamson, Physical Chemistry of Surfaces,
>> John Wiley and Sons, 1990", so if you can get a copy of the book you'll find a
>> better and longer explanation.
>>
>> HTH
>>
>
>
>
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-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project