[QE-users] O_ad(O-adsorption) is not binding at bridge position on Pt-surface

[Ari P Seitsonen]

Dear Venkataramana Imandi,

   Possibly the bridge site is a saddle point but the symmetry is not 
perfect, so the symmetry constrain does not fix the atom from moving 
toward a lower-energy site. I would try arranging the surface so that for 
example the x axis is the reaction coordinate for diffusion from a 
three-fold site to the other three-fold site, and then fixing the value of 
that coordinate (well, I do not remember if the fixed coordinates in the 
input are for relative or Cartesian coordinates, but you could try fixing 
a Cartesian one). If the bridge would be, however, a in-principle fully 
symmetric coordinate it does not get fixed because the symmetries are not 
found.

     Greetings from Rüschlikon (ZH),

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
     Ecole Normale Supérieure (ENS), Département de Chimie, Paris
     Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Tue, 10 Apr 2018, Venkataramana Imandi wrote:

> 
> Dear QE community,
> 
> I am a new user of Quantum espresso simulation package. I installed 6.2.1 Quantum espresso in the
> Linux-X86_64-INTEL-MPI. I want to find out the binding energy of O_ad at various sites(top,bridge,hcp
> and fcc) on Pt-surface and Pt-Ni alloy surface. In the beginning, i have tried on Pt-surface, and I got
> O_ad at top, hcp and fcc sites on Pt-surface, however, i couldn't find O_ad at bridge position.
> I have tried all possible ways of getting O_ad at the bridge position(between Pt-Pt). None of them were
> given succussful results, and the resulted O_ad comes to either fcc or hcp position. All possible ways:
> using with and without spin-polarization, davidson diagonalization anc cg, option (nosym = .TRUE. and
> .FALSE.), mixing mode(plain, local-TF and TF), changing mixing-beta(0.2, 0.3 and 0.5), neutral,
> negative charge(-2) and different simulation setup (present 24 atoms to 48 Pt atoms). The last option,
> i used different pseudopotential(Pt.pw91-n-van.UPF and O.pw91-van_ak.UPF), herein, i got error as
> follows (Error in scalartorealdp  Too few elements found). Now i stopped trials.
> I ask you can anyone do calculation in your simulation setup with the given input file, tell me the
> where the problem is.
> 
> I really thanks to you in advance for any suggestions regarding this.
> For information, i used VASP in the last year, therein, i obtained O_ad at all sites on Pt-surface.
> 
>  &control
>     calculation='relax'
>     restart_mode='from_scratch',
>     pseudo_dir = '/home2/oth/ch18ipf01/pseudopotential2/',
>     prefix='pt'
>     tprnfor = .true.,
>     nstep = 200
>  /
>  &system
>     ibrav=0,
>     nat=25,
>     ntyp=2,
>     ! nspin = 2,
>     ! starting_magnetization(1)=0.7,
>     ecutwfc = 32.0,
>     ecutrho = 320.0,
>     occupations='smearing',
>     smearing='methfessel-paxton',
>     degauss=0.02
>    ! tot_charge = -2,
>     nosym = .TRUE.
>  /
>  &electrons
>     diagonalization='cg'
>     conv_thr = 1.0e-6
>     mixing_beta = 0.3
>    electron_maxstep = 1000
>  /
> &ions
> ion_dynamics='bfgs',
>  /
> ATOMIC_SPECIES
> Pt  195.084  Pt.pbe-nd-rrkjus.UPF
> O    15.999  O.pbe-rrkjus.UPF
> 
> ATOMIC_POSITIONS {angstrom}
> O     3.45091550          1.17466050         13.69732100  1 1 1
> Pt    4.84778787          1.20016667         12.44963917  1 1 1
> Pt    3.46185858          3.60066659         12.44963917  1 1 1
> Pt    2.07592929          1.20016667         12.44963917  1 1 1
> Pt    0.69000000          3.60066659         12.44963917  1 1 1
> Pt    3.46185858          0.40000000         10.18642611  1 1 1
> Pt    4.84778787          2.80049996         10.18642611  1 1 1
> Pt    0.69000000          0.40000000         10.18642611  1 1 1
> Pt    2.07592929          2.80049996         10.18642611  1 1 1
> Pt    3.46185858          2.00033330          7.92321305  1 1 1
> Pt    4.84778787          4.40083326          7.92321305  1 1 1
> Pt    0.69000000          2.00033330          7.92321305  1 1 1
> Pt    2.07592929          4.40083326          7.92321305  1 1 1
> Pt    4.84778787          1.20016667          5.66000000  1 1 1
> Pt    3.46185858          3.60066659          5.66000000  1 1 1
> Pt    2.07592929          1.20016667          5.66000000  1 1 1
> Pt    0.69000000          3.60066659          5.66000000  1 1 1
> Pt    3.46185858          0.40000000          3.39678694  0 0 0
> Pt    4.84778787          2.80049996          3.39678694  0 0 0
> Pt    0.69000000          0.40000000          3.39678694  0 0 0
> Pt    2.07592929          2.80049996          3.39678694  0 0 0
> Pt    3.46185858          2.00033330          1.13357388  0 0 0
> Pt    4.84778787          4.40083326          1.13357388  0 0 0
> Pt    0.69000000          2.00033330          1.13357388  0 0 0
> Pt    2.07592929          4.40083326          1.13357388  0 0 0
> 
> K_POINTS {automatic}
> 3 3 1 0 0 0
> CELL_PARAMETERS {angstrom}
> 5.5437171600     0.0000000000     0.0000000000
> 0.0000000000     4.8009999000     0.0000000000
> 0.0000000000     0.0000000000    25.5792783300
> 
> 
> With best regards
> Venkataramana Imandi
> Postdoctoral fellow
> IIT Madras, India.
> 
>                                                                                                      
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> 
> 
> 
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>