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Molecular Dynamics simulations Surface interaction energy

  1. Jan 8, 2012 #1
    I've simulated a solid metal cluster of gold fcc100
    And a surface Platinum in fcc111 using a classical mechanical approach.
    Do you think i could get the surface free energies(the ones to use in determining the Wulff shape) from periodic boundary conditions and if so how? Im really confused, i need to make an approximation of the height and width of the melted particle so i would like the energy in the UP/z direction.

    The gold cluster is cubic at the initial state btw.
  2. jcsd
  3. Jan 8, 2012 #2
    Surface energies can be obtained using a slab model in which you orient the surface of interest to be normal to z-axis (for example). You apply periodic boundary conditions in x and y but in z-direction you have two options. Either still using periodic boundary conditions but leave a vacuum gap above the surface of a thickness > 1nm (a convergence test is needed here) or if you are using classical potentials you can actually remove the periodicity in z and use a vacuum boundary condition in this direction. IN that case
    Esurf=(Eslab-Ebulk)/2 , The factor of two because you have two exposed surfaces.

    The nanoparticle/ cluster approach you described above is not common and indeed may not always be useful to calculate the surface energy beacause:
    1- All the faces of the cluster should represent the same surface. This is very hard to achieve unless the material has a crystal structure of high symmetry.
    2- One may need a very large cluster to guarantee convergence.
  4. Jan 8, 2012 #3
    Hi again,
    Thank you for the clear answer.
    I just want to estimate the energies for determining how high and wide the cluster will be at some state.
    I simulate an actual surface with an on it resting cluster, and not a potential difference, so it is a bit more coumbersome i think.

    But how will i determine the wulff shape from the initial state, i have only 6 faces and to me it looks like it will be a triangle(3d). Do you have any litterature to recommend, this stuff is mabye not so much at my level(undergraduate).

    Thanks again
    Btw. it is the contanct energy between cluster and surface which is interesting
    Last edited: Jan 8, 2012
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