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.seitso...@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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