[Pw_forum] "Centering" Requirement of ESM

[Lorenzo Paulatto]

It doesn't require symmetry: it requires NO symmetry. Which is actually the
opposite of what you seem to think.

Kind regards

-- 
Lorenzo Paulatto
Written on a virtual keyboard with real fingers

On 29 Jul 2017 2:14 p.m., "Robert Molt" <r.molt.chemical.physics at gmail.com>
wrote:

> 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 setting nosym <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 setting nosym <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
> ------------------------------------------------------------
> ---------------------------------------------
>
> On Jul 29, 2017, at 5:15, Lorenzo Paulatto <lorenzo.paulatto at impmc.upmc.
> fr> <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@
> 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 setting nosym <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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