[QE-users] recommended methods for slab calculations

[Michal Krompiec]

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
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>
>
> GIUSEPPE MATTIOLI
> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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> E-mail: <giuseppe.mattioli at ism.cnr.it>
>
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