[QE-users] recommended methods for slab calculations

[Tobias Klöffel]

Dear Michal,

if resource usage is important, did you check what happens without any 
special treatment and just use a vacuum of 25-35 bohr? Most of the time 
it is sufficient to do so without any assume_isolated flag.

Best,
Tobias

On 4/3/20 3:04 PM, Michal Krompiec wrote:
> Dear Giuseppe,
> Thank you!
> Best,
> Michal
>
> On Fri, 3 Apr 2020 at 12:00, Giuseppe Mattioli
> <giuseppe.mattioli at ism.cnr.it> wrote:
>>
>> Dear Michal
>> I'm a fan of esm. If you want to study the adsorption of molecules
>> inducing a strong vertical dipole you are forced to decouple such
>> dipole along the z direction of the cell, otherwise you experiment an
>> horrible "capacitor effect" on the potential curve. To use esm='bc1'
>> (a vacuum-slab-vacuum geometry) you need to confine the electronic
>> density of your system (the density, not the atoms...) between -l/4
>> and l/4 (you can shift the 0 of the cell if you don't want to shift
>> the atoms), where l is the z edge of your supercell. I don't know if
>> you consider this as an "enormous vacuum padding"...
>>
>> Moreover, esm produces "for free" a very useful file (in the TMP_DIR),
>> namely prefix.esm1, where at the end of each scf iteration useful
>> quantities are plotted, such as the electrostatic potential and the
>> charge density integrated on x,y planes. You may want to have a look
>> to this recent paper (J. Phys. Chem. C 2020, 124, 3601) to see what
>> you can do with such data (e.g., calculate changes in the surface
>> workfunction upon the adsorption of polar molecules).
>>
>> Finally, during the first scf iteration you may experiment a bit of
>> instability, but it is generally not a dramatic problem...
>>
>> HTH
>> Giuseppe
>>
>>
>> Quoting Michal Krompiec <michal.krompiec at gmail.com>:
>>
>>> Hello,
>>> I was wondering which assume_isolated method is the preferred choice
>>> for calculation of adsorption energies of small molecules on 2D slabs
>>> of metals and oxides.
>>> So far, I've been using assume_isolated='2d', but it requires an
>>> enormous vacuum padding. Is esm less resource-hungry? Does anyone use
>>> a less accurate scheme first (e.g. no "assume_isolated" and a small
>>> vacuum padding) and moves later to the target large cell with
>>> assume_isolated=2d?
>>> I understand that it all depends on the system, and that a convergence
>>> test has to be done anyway, but I would be grateful for any tips.
>>>
>>> Thanks,
>>> Michal Krompiec
>>> Merck KGaA
>>> _______________________________________________
>>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
>>> users mailing list users at lists.quantum-espresso.org
>>> https://lists.quantum-espresso.org/mailman/listinfo/users
>>
>>
>> GIUSEPPE MATTIOLI
>> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
>> Via Salaria Km 29,300 - C.P. 10
>> I-00015 - Monterotondo Scalo (RM)
>> Mob (*preferred*) +39 373 7305625
>> Tel + 39 06 90672342 - Fax +39 06 90672316
>> E-mail: <giuseppe.mattioli at ism.cnr.it>
>>
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
>> users mailing list users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users


-- 
M.Sc. Tobias Klöffel
=======================================================
HPC (High Performance Computing) group
Erlangen Regional Computing Center(RRZE)
Friedrich-Alexander-Universität Erlangen-Nürnberg
Martensstr. 1
91058 Erlangen

Room: 1.133
Phone: +49 (0) 9131 / 85 - 20101

=======================================================

E-mail: tobias.kloeffel at fau.de