[QE-users] recommended methods for slab calculations

[Weitzner, Stephen Eric]

Michal,

In addition to ESM (which, by the way, you should set nosym = .TRUE. when you use this method), you should also take a look at the electrostatic PBC corrections introduced by the Environ module (http://www.quantum-environ.org). Documentation for the methods in this module can be found on that website.

Best,
Steve

-- 
Stephen Weitzner, PhD
Postdoctoral Research Scientist
Quantum Simulations Group
Lawrence Livermore National Laboratory
 
T : (925) 422-4449
E : weitzner1 at llnl.gov



On 4/3/20, 7:00 AM, "users on behalf of Giuseppe Mattioli" <users-bounces at lists.quantum-espresso.org on behalf of 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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