Work functions at interfaces

This tutorial will show how to use BAND to calculate the work function Φ of the

  • Al(100)/vacuum interface

  • Al(100)/LiF(100) interface

/scm-uploads/doc.2023/Tutorials/_images/preview19.png

Fig. 41 Plane-averaged electrostatic (Coulomb) potential vs z coordinate. The orange horizontal line is the Fermi energy. The red and green vertical lines indicate how the work function is calculated on either side of the slab. The work function (WF) for the Al(100)/vacuum interface (green) is 4.33 eV. The WF for the Al(100)/LiF(100) interface (red) is 3.63 eV.

The adsorption of LiF(100) will decrease the work function, as compared to vacuum. The results will be compared to plane-wave-DFT results by Prada S., et al. 1 and Kondo and Matsushista 2

Al(100) Φ [eV]

Al(100)/LiF(100) ΔΦ [eV]

functional

code

Prada et al.

4.37

-0.7

PW91

VASP

Kondo and Matsushista

4.28

-0.59

PBE

Quantum ESPRESSO

This tutorial

4.33

-0.70

PW91

BAND

Note

The above works differ not only in code and functional, but also basis set, k-point sampling, number of layers in the Al or LiF slabs, whether the system is relaxed or not, …

Start AMSinput
Switch to BAND: ADFPanel → BANDPanel

When setting up a solid-solid interface, the lattice constants must match. Both Al and LiF are cubic, so if their lattice constants match, also the (100) surface lattice constants will match. At least one of the materials needs to be a bit strained. Here, we will strain the LiF slab to match the Al slab. We will place the LiF slab at a distance of 3.27 Å from the Al slab.

Note

For other interfaces, you may need to apply surface rotations and use surface supercells if the lattice constants of the two materials are very different, in order to not apply too much strain to one of the materials.

Download the LiF-on-Al.xyz file

Select File → Import Coordinates and select the downloaded file

/scm-uploads/doc.2023/Tutorials/_images/interface.png

Then, set the BAND settings:

XC functional: GGA → PW91
Basis set: DZP
Details → Numerical Quality
Integration: Becke Good
Spline Zlm fit: Good
/scm-uploads/doc.2023/Tutorials/_images/numqual.png
Click the MoreBtn next to K-space
Number of points: 7 7
/scm-uploads/doc.2023/Tutorials/_images/k_space.png
Details → SCF
Electronic temperature: 0.002 hartree
/scm-uploads/doc.2023/Tutorials/_images/eltemp.png

This sets up a 7x7 k-space grid. The integration, spline zlm fit, and electronic temperature options help with the SCF convergence.

Save and run the job.

File → Save As with a new name
Run the job

To get the work function:

Download WorkFunctionVacuumAndInterface.py
Modify the results_dir variable to give the correct path to the .results folder from the previous calculation. It should contain two files: ams.rkf and band.rkf.
Open a terminal and run the script as $AMSBIN/amspython WorkFunctionVacuumAndInterface.py

This produces a plot like the below:

/scm-uploads/doc.2023/Tutorials/_images/preview19.png

Fig. 42 Plane-averaged electrostatic (Coulomb) potential vs z coordinate. The orange horizontal line is the Fermi energy. The red and green vertical lines indicate how the work function is calculated on either side of the slab. The work function (WF) for the Al(100)/vacuum interface (green) is 4.33 eV. The WF for the Al(100)/LiF(100) interface (red) is 3.63 eV.

1

  1. Prada, U Martinez, G. Pacchioni. Work function changes induced by deposition of ultrathin dielectric films on metals: A theoretical analysis. Phys. Rev. B. 78, 235423. DOI: 10.1103/PhysRevB.78.235423

2

  1. Kondo, T. Matsushista. Vacuum-Level Shift at Al/LiF/Alq3 Interfaces: A First-Principles Study. ACS Omega 2019, 4, 8, 13426–13434. https://doi.org/10.1021/acsomega.9b01667