[Wien] top, hollow and bridge interface calculations

[morteza rafiee]

    Dear users
      I am performing interfaces calculations. I created symmetric  substrate layers and deposited a mono layer on it within top, bridge and hollow  sites configurations. Then I relaxed the slab for these three various states,  i.e. top, bridge and hollow sites. 
      First I would report that I have found to be the total  energy of the bridge site smaller than the other top and hollow sites. This is  in the case that, unfortunately, our deposited atoms for the later case of  bridge site are under pressure in both x and y directions as well as z  direction, i.e. :FGLxxx and :FORxxx are nonzero for x, y and z directions. For  the top and hollow sites, however, there are no forces in x and y directions. For  these two cases, top and hollow sites, we have only, as expected, non zero  forces in z direction. 
      Trying has been made to reach the stable configuration using  relaxation. But we could not reach the zero forces in x and y directions for  the case of bridge site.
           
  Now our questions are:
      Do we try to study bridge site at all? This question is raised  due to the fact that we could not find zero forces for x and y direction even  after relaxation. This itself indicates that most likely our atomic positions  are not consistent with space group of the substrate. 
      For sure in the case of bridge site sgroup program also complain  about the space group. We did not pay attention to the message of sgroup  program, because we believe that we have already correctly created the  structure.
      If we do not, how we can explain the calculated smaller  energy for the case of bridge site compared to the other cases.
           
  We also, furthermore, do not know what criterion is for  choosing an initial distance between our substrate and deposited layer. If we  know the answer of this question, then we hope to be far away of local minimum to  avoid trapping on it and also save relaxation time.
      Our relaxations are still running, but we would below report  at this stage our results.
      Our forces and total energy after relaxation for the case  of:
      1) Top site
      :FGL001:   1.ATOM                 0.000000000     0.000000000     0.433000000
      :FGL002:   2.ATOM                 0.000000000     0.000000000    -3.354000000
      :FGL003:   3.ATOM                 0.000000000     0.000000000    -1.251000000
      :FGL004:   4.ATOM                 0.000000000     0.000000000     0.847000000
      :FGL005:   5.ATOM                 0.000000000     0.000000000     0.339000000
      :FGL006:   6.ATOM                 0.000000000     0.000000000     0.760000000
      :FGL007:   7.ATOM                 0.000000000     0.000000000     0.408000000
      :FGL008:   8.ATOM                 0.000000000     0.000000000     0.321000000
      :FGL009:   9.ATOM                 0.000000000     0.000000000    -5.245000000
      :ENE  : **********  TOTAL ENERGY IN Ry =       -92995.521365
       
      2) Hollow site
      :FGL001:   1.ATOM                 0.000000000     0.000000000    -1.725000000
      :FGL002:   2.ATOM                 0.000000000     0.000000000     3.962000000
      :FGL003:   3.ATOM                 0.000000000     0.000000000    -0.246000000
      :FGL004:   4.ATOM                 0.000000000     0.000000000    -7.898000000
      :FGL005:   5.ATOM                 0.000000000     0.000000000    -0.219000000
      :FGL006:   6.ATOM                 0.000000000     0.000000000    -0.190000000
      :FGL007:   7.ATOM                 0.000000000     0.000000000     0.893000000
      :FGL008:   8.ATOM                 0.000000000     0.000000000     0.458000000
      :FGL009:   9.ATOM                 0.000000000     0.000000000     3.963000000
      :ENE  : **********  TOTAL ENERGY IN Ry =       -92995.561715
       
      3) Bridge site
      :FGL001:   1.ATOM                -4.488321022     4.488320993     1.420000000
      :FGL002:   2.ATOM                 4.624575687    -4.624575656     0.037000000
      :FGL003:   3.ATOM                 0.174937133    -0.174937132    -1.701000000
      :FGL004:   4.ATOM                 0.092376044    -0.092376043    -1.618000000
      :FGL005:   5.ATOM                -0.034641016     0.034641016    -2.211000000
      :FGL006:   6.ATOM                -0.012701706     0.012701706    -0.588000000
      :FGL007:   7.ATOM                 0.076210236    -0.076210236     0.359000000
      :FGL008:   8.ATOM                -0.048497423     0.048497423     0.270000000
      :FGL009:   9.ATOM                -0.386247333     0.386247330     0.792000000
      :ENE  : **********  TOTAL ENERGY IN Ry =       -92995.657796
       
      I will be thankful to every body that helps me. 
      Morteza Rafiee
       
    
 
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