[Pw_forum] modeling open-shell molecules on metal surfaces

[Guido Fratesi]

Dear Sergi Vela,

are you really sure about input coordinates?
I executed "xcrysden --pwi Test.input" and found a rather strange structure!

Also, do you really need to use ibrav=0 with the axes as you defined? It 
the substrate is Au(111) you could use a more symmetric unit cell.

Then: k-point mesh seems to me too coarse (if that was not intentional 
for testing)

HTH
Guido

On 03/02/2015 10:57, Sergi Vela wrote:
> 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.
>
>

-- 
Guido Fratesi

Dipartimento di Fisica
Universita` degli Studi di Milano
Via Celoria 16, 20133 Milano, Italy