1. Practice #4: defect NST551 TA : Lee Jounghee leejhk@kaist.ac.kr

2. Supercell structure 1.To make detect-system, the supercell structure have to be made at first. 2.Modify 'input' file where is in same directory with CONTCAR. 3.Create supercell's atomic coordinate (file 'poscar.xyz') > poscar.x 4.Extend cell size in POSCAR and replace the atomic position part with supercell's atomic coordinate in 'poscar.xyz' and 1 C 2 6 6 1 Super cell size (xyz) supercell size supercell's atomic coordinate

3. Supercell structure 6x6x1 graphene4x4x4 Si

4. 1.Remove a defect atom for one of the original atoms(C, Si) in supercell structure. Defect system calculation(vacancy) Remove line for a carbon atom from original supercell

5. 1.Substitute a defect atom(N) for one of the original atoms(C, Si) in supercell structure. Defect system calculation (substitutional) Add defect atom term in POSCAR ex) 1 N atom, 71 C atoms Original atomic position Defect atomic position Break symmetry for atomic position when the defect atom is added. ex) 11.10599995 9.36185417 10.00000000  11.20599995 9.36185417 10.00000000

6. Defect system calculation N-doped grapheneN-doped Si N

7. Defect system calculation N-doped grapheneN-doped Si

8. 2.Add pseudo potential part of defect atom in POTCAR (same order in POSCAR file). You can find pseudo potential files of every atoms following directory /users/nst551/build/vasp-potentials/PAW_PBE/ 3.Run scf calculation (get CHGCAR). 4.Run non-scf calculation to plot DOS. Nitrogen's pseudo potential part in POTCAR Defect system calculation (substitutional)

9. DOS of N doped defect systems graphene Si

10. Defect formation energy means whether the system with defects is more stable or unstable than the bulk system. Defect formation energy E formation (eV) = E(defect system) – [N bulk  bulk + N defect  defect ] E(defects system) : Total energy of system with defects N bulk : Number of bulk atoms  bulk : chemical potential of bulk atoms N defect : Number of defects  defect : chemical potential of defects E f, N-doped graphene = E(N-doped graphene) – [N C  C + N N 1/2  N 2 ],  defect = 1/2  N 2 E f, N-doped Si = E(N-doped Si) – [N Si  Si + N N 1/2  N 2 ],  defect = 1/2  N 2 E(defect system)  bulk N  defect Defect formation energy N-doped graphene-664.65-9.23071-8.25-1.068 N-doped silicon-695.11-5.420127-8.251.48 (units: eV) Defect formation energy

11. Practice #4 1.Make supercell and defect structures for graphene and Si. 2.Plot DOS and find defect states and find defect formation e nergy for graphene and Si. ( ~11/13)