![]() A polar termination will lead to a very high surface energy, so we can skip Secondly,įor structures containing oxidation states, we need to ensure that our surfaces are In our slab rather than the surface energy for one slab in our calculation. Symmetric), we would be calculating the average surface energy of two different surfaces If the surfaces are different (the slab is not Same as the above equation for surface energy is used to get the energy of one surface, It's important that both surfaces are the Property of our slab object to check this. To do this, we need to ensure the slab model has Laue First off, we need to ensure that all slabs we will be calculating have There are a couple of rules before we actually run calculations on some of these weighted_surface_energy, ) ) # If we want to see what our Wulff shape looks like wulffshape. lattice, miller_list, e_surf_list ) # Let's get some useful information from our wulffshape object print ( "shape factor: %.3f, anisotropy: \ %.3f, weighted surface energy: %.3f J/m^2" % ( wulffshape. values () # We can now construct a Wulff shape with an accuracy up to a max Miller index of 3 wulffshape = WulffShape ( Ni. keys () e_surf_list = surface_energies_Ni. The total energy of the bulk ($E_ miller_list = surface_energies_Ni. To do this, we actually need to calculate (from first principles) the total energy of two structures. all_slabs = generate_all_slabs ( Si, 3, 10, 10 ) print ( " %s unique slab structures have been found for a max Miller index of 3" % ( len ( all_slabs )) ) get_slabs ())) ) # The simplest way to do this is to just use generate_all_slabs which finds all the unique # Miller indices for a structure and uses SlabGenerator to create all terminations for all of them. cubic ( 5.46873 ) Si = Structure ( lattice, ,, ,, ,, ,, , ], ) slabgen = SlabGenerator ( Si, ( 1, 1, 1 ), 10, 10 ) print ( "Notice now there are actually now %s terminations that can be \ generated in the (111) direction for diamond Si" % ( len ( slabgen. # Let's try this for a diamond Silicon structure lattice = Lattice. get_slabs () print ( "The Ni(111) slab only has %s termination." % ( len ( all_slabs ))) For a # fcc structure such as Ni however, there should only be one way to cut a (111) slab. The # simplest example of this would be the Si(Fd-3m) (111) slab which can be cut or # terminated in two different locations along the vector of the Miller index. When generating a slab for a particular orientation, there are sometimes # more than one location we can terminate or cut the structure to create a slab. This returns a LIST of slabs rather than a single # slab. Plug in the CONVENTIONAL unit cell of your structure, the # maximum Miller index value to generate the different slab orientations along # with the minimum slab and vacuum size in Angstroms slabgen = SlabGenerator ( Ni, ( 1, 1, 1 ), 10, 10 ) # If we want to find all terminations for a particular Miller index orientation, # we use the get_slabs() method. Therefore, synthesizing (201) and (100) nanosheets will greatly improve the electrochemical properties of the material.# We'll use the SlabGenerator class to get a single slab. In addition, lower surface band gaps are found in all orientations compared to the bulk one, which indicates that electrical conductivity can be improved significantly by enlarging surfaces with relatively low band gaps in the particle. Therefore, the Li migration rate on surfaces could be effectively increased by maximizing the exposure of these low redox potential surfaces. Surfaces (100), (010) and (201) present lower Li surface redox potentials in comparison with the bulk material. It suggests that the Wulff shape of LiVOPO4 is closely related to the chemical environment around. Similar calculations for VOPO4 display a larger decrease in surface energies for the (100) surface rather than those in the other surfaces. The (001) and (111) orientations are the dominating surfaces in the Wulff shape. Thermodynamic equilibrium shape of the LiVOPO4 crystal is built with the calculated surface energies through a Wulff construction. Relatively low-energy surfaces are found in the (100), (010), (001), (011), (111), and (201) orientations of the orthorhombic structure. First principles calculations were used to investigate the surface energies, equilibrium morphology, surface redox potentials, and surface electrical conductivity of LiVOPO4. ![]()
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