VASPMod1

Periodic Boundary Conditions-Local Optimization of Bulk Gold and Gold surfaces with DFT

Part 3: Creating a Slab

In this part, you will tranform your bulk gold (infinite in 3 dimensions) into a slab (infinite in 2 dimensions).
In the third dimension, the resulting surface is exposed to vacuum.
You will consider the stability of different cuts of the bulk materials.

1. You'll be working in the directory VASPMod1/Slab.
2. In this directory are two directories with larger bulk structures called fcc100bulk and fcc111bulk. Optimize the lattice constants of both of these structures with the ISIF=3 tag as you did in previous parts.
3. Next we will take these optimized bulk structures and convert them into slabs where one dimension is exposed to vacuum. The slab for the fcc (111) structure is already set up for you and is in the directory called Slab111. Optimize the slab and get its energy. No change is needed. Note that you are no longer optimizing the lattice constants. So you only need to optimize these structures until the last force is less than your convergence criteria.
4. The directory called Slab100 has all VASP starting files except for the POSCAR. You need to create the slab from your optimized bulk structure in fcc100bulk by following these steps:
   
   1. First copy the CONTCAR file in fcc100bulk into the directory, Slab100 and open it with ase gui.
   2. Go to View >> Repeat ... , repeat twice in all directions then click "Set unit cell". Your box now should contain 32 atoms.
   3. Select the bottom two layers (two layers with the lower z-values) and go to Tools >> Constraints ... and click "Fix" selected atoms. This is how you constrain atoms.
   4. Save your POSCAR and exit ase gui. Then open the POSCAR with vim, find the third lattice vector, increase its third element by 8. This is how you add 8 Angstroms of vacuum.
5. Relax the slab. (Don't forget to apply constraints!)