[Pw_forum] modeling open-shell molecules on metal surfaces

[Sergi Vela]

Hi all,

I'm having a lot of troubles in modeling the adsorption of molecules on
surfaces. I've quite a lot of experience with QE when working with crystals
made of open-shell molecules but I'm not familiar with the description of
metal surfaces.

First of all, I'm using Qespresso v.5.1.1

I succeed in simulating 4 layers of a 111 Gold surface with Quantum
Espresso (QE). However, using the same surface and unit cell, when I
include a magnetic (open-shell) molecule on top of that surface, even if
its far away from it, I cannot reach convergence. I'm 99% sure that the
input is fine in terms of the unit cell definition (see input file
attached) and the problem is just the convergence of the electronic
structure.

I believe the problem is the fact that the system is highly inhomogeneous
as it has a metal surface and an open-shell molecule. I take as an example
the smearing, since, although it is mandatory when modeling the metal
alone, it seems to hinder the description of an open-shell molecule.
Originally, I used methfessel-paxton smearing with a 'degauss' of 0.2 eV.
The convergence seems to be even worse as the value is increased, and
changing the type of smearing doesn't help neither.

I've tried several tricks to try to improve electronic structure's
convergence. Changing the 'mixing_beta', the 'type of mixing', removing the
smearing, switching to 'cg' algorith, increasing number K points ... all of
them with identical output (take Summary.out as an example of the typical
evolution of the SCF energy, you'll see that is awful).

Anyone has experience on modeling such king of systems?

Any help is appreciated, thanks in advance

Dr. Sergi Vela,
University of Strasbourg, France.
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