[Pw_forum] "Centering" Requirement of ESM

[Robert Molt]

I appreciate the help. If ESM does not require this symmetry, can you 
explain what is meant by the manual's statement of:

:

"Requires cell with a_3 lattice vector along z,

normal to the xy plane, with the slab centered around z=0. Also requires symmetry checking to be
      disabled along z, either by settingnosym 
<http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#nosym>  = .TRUE.
      or by very slight displacement (i.e., 5e-4 a.u.)
      of the slab along z."


I want to make sure I am in compliance with the manual's specifications, 
and I clearly must not understand what that means if I misinterpreted it 
to mean it requires symmetry along the z axis.


Separately, given that we have no symmetry in xy, is it logically 
necessary to "cap" boundary atoms with hydrogens (or the like) to avoid 
artifacts at the boundary?


On 7/28/17 6:41 PM, 大谷実 wrote:
> Dear Robert,
>
> Besides Lorenzo’s message, I can add one more thing. ESM does not 
> require symmetry along z-axis, so you do not need to put an additional 
> adsorbate molecule on the bottom.
>
>>     Also requires symmetry checking to be
>>           disabled along z, either by settingnosym
>>     <http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#nosym>  = .TRUE.
>>           or by very slight displacement (i.e., 5e-4 a.u.)
>>           of the slab along z.
>>
>
>
> Best regard,
> Minoru
> --------------------------------------------------------------------------------------------------------
> Minoru Otani
> National Institute of Advanced Industrial Science and Technology
> Research Centre for Computational Design of Advanced Functional Materials
> email : minoru.otani at aist.go.jp <mailto:minoru.otani at aist.go.jp>
> ---------------------------------------------------------------------------------------------------------
>
>> On Jul 29, 2017, at 5:15, Lorenzo Paulatto 
>> <lorenzo.paulatto at impmc.upmc.fr> wrote:
>>
>> It does not matter, it is only need to be roughly centered
>>
>> -- 
>> Lorenzo Paulatto
>> Written on a virtual keyboard with real fingers
>>
>> On 28 Jul 2017 9:36 p.m., "Dr. Robert Molt Jr." 
>> <r.molt.chemical.physics at gmail.com 
>> <mailto:r.molt.chemical.physics at gmail.com>> wrote:
>>
>>     Good evening,
>>
>>     I am confused by the "centering" requirements of ESM. It is
>>     stated that:
>>
>>     Requires cell with a_3 lattice vector along z,
>>           normal to the xy plane, with the slab centered
>>           around z=0. Also requires symmetry checking to be
>>           disabled along z, either by settingnosym
>>     <http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#nosym>  = .TRUE.
>>           or by very slight displacement (i.e., 5e-4 a.u.)
>>           of the slab along z.
>>
>>     I have constructed a slab which is symmetric about the xy plane
>>     and centered around z=0 contour. This is fine and good.
>>
>>     However, once I add the adsorbate molecule, I cannot have
>>     symmetry...unless it is intended that I add the same adsorbate
>>     molecule on the "bottom" of the simulation, too? I am unclear
>>     what is meant by the slab being "centered." Center of mass?
>>     Center of symmetry?
>>
>>
>>
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