In this new tutorial, I'll be showing you how to use Quantum Espresso and Density Functional Theory (DFT) to calculate the adsorption energy of a molecule on a surface/slab using the water molecule (H2O) on a lithium hydride (LiH) surface as an example. This is a really important calculation in surface science and catalysis research.
We'll be following a paper from 2017 that looked at this same system using various computational methods. I've downloaded the structure files they provide in the supplementary info. To keep things simple, we'll use the one with 32 atoms in the LiH slab and 3 atoms for the water molecule.
I'll walk through setting up the calculation in my favorite Quantum Espresso GUI called BURAI. This involves choosing the right pseudopotentials, setting the energy cutoffs, and a few other key parameters.

Paper link: https://pubs.aip.org/aip/jcp/article/...

CIF File: https://www.bragitoff.com/wp-content/...

Input and Output files: https://www.bragitoff.com/wp-content/...

To get the adsorption energy, we actually need to run 3 separate calculations - one for the full H2O-LiH system, one for just the isolated H2O molecule, and one for just the LiH slab. I'll show you how to set up and run each of these calculations step-by-step in BURAI.
Once those are done, I'll demonstrate how to extract the total energies from the output files and use them to calculate the final adsorption energy value according to the formula in the paper. We'll then compare our result to what they reported and discuss any differences.