Objectives

• Calculate surface formation energy for the (111) surface in FCC aluminum
• Perform K-Point convergence
• Only one K-Point is needed in the direction perpendicular to the surface
• Plot surface formation energy vs. K-Point grid
• Perform Convergence study on the number of layers parallel to the surface
• This can be achieved through the provided surface structure generation script
• Only increase the number of layers parallel to surface while keeping the atomic layers parallel to the other two directions constant
• Plot surface formation energy vs. number of layers
• Investigate the effect of the length of the vacuum
• Use converged K-Point grid and layer amount
• Use the script provided to change the length of the lattice translation vector perpendicular to the surface and calculate the surface formation energy
• PLot surface formation energy vs. length of vacuum

Preperation

Step 1

• Obtain two INCAR files and a KPOINTS file from here and save them separately.
• Give the two INCAR files different names such as "INCAR_Rel" and "INCAR_sta"
• Retrieve the VASP executable and the POTCAR (specific to your group) from where it was saved for the previous section in this homework.
• As before, collect all these files into the same directory

Step 2

• Copy this python code and save it with the file extension ".py".

Running the Calculation

Overview

This calculation is split into two parts

Part 1

• Use the provided python script to generate a POSCAR file with a supercell of at least 5x5x5 atoms.
• Retrieve the relaxation INCAR file and rename it to just "INCAR"
• Run VASP using the provided PBS script and job file.

Part 2

• Find the output file called "CONTCAR" from the previous part. Rename that file "POSCAR".
• Get the static INCAR file saved previously and rename it to "INCAR"
• With the same POTCAR and K-Points files from before run VASP.

K-Point Convergence

• Using the BASH script from the section 1 of this homework, perform the same K-Point mesh convergence.

Vacuum Convergence

• Create several POSCAR files using a range of vacuum lengths
• Run VASP for each and investigate the effect, vacuum length has.

Guidelines for accurate surface energy calculation

Once the calculations have been completed, locate the OSZICAR output file. It contains data from each electronic step. Extract the final energy Esurf with the following command:

tail -n1 OSZICAR|awk '{print \$5}'


Use the following formula to calculate surface formation energy

$E_{surf-from} = \frac{E_{surf}-N\epsilon}{2A}$

Where Esurf is the total energy of the simulation box with the surface, N is the number of atoms in the simulation box, $\epsilon$ is the cohesive energy per atom of the bulk structure, and A is the area of the surface.

By using the codes provided here you accept the the Mississippi State University's license agreement. Please read the agreement carefully before usage.