Hello,
I am trying to run a cluster expansion for expressing the formation energy of O atoms adsorbing to a Pt surface (slab model). I am replicating published work (DOI: 10.1039/c4cy00763h) and am not able to get similar ECI values to those reported, despite using the same clusters and all of the same calculation parameters. Of particular confusion is the empty site ECI, as the value I obtain (~0.2) is vastly different to that reported in the paper (~0.6), despite the calculated formation energy of the clean surface being in good agreement (the end points of the convex hull also match the literature, with the use of ref_energy.in)
I had assumed that the empty site ECI should be essentially the same as the formation energy for the empty site structure, which it is for the literature ECI but not for mine (my calculated and fitted energy for the empty site structure are ~0.6). Is someone able to explain how to interpret the ECI, particularly in terms of the empty site ECI and the relationship to the formation energy of the empty site structure?
I hope this makes sense, files can be provided on request.
Kind regards,
Anna
Empty Site Energy Correction Index (ECI) is a parameter used in the context of alloy cluster expansion techniques, specifically in the Cluster Expansion Method (CEM) for studying materials with substitutional disorder. An empty site refers to a lattice site in a crystal structure that is unoccupied by any atom. The ECI associated with an empty site represents the change in energy of the system when an atom occupies that site, relative to the case when the site is empty.
Interpreting an empty site ECI involves understanding its magnitude and sign:
Magnitude:
Positive ECI: A positive ECI indicates that the system’s energy increases when an atom occupies an empty site. This might suggest that the empty site is not favorable for occupation, and the system prefers to have the site unoccupied.
Negative ECI: A negative ECI means that the system’s energy decreases when an atom occupies an empty site. In this case, the empty site is energetically favorable for occupation, and the system prefers to have the site occupied by an atom.
Sign:
Positive Sign: A positive sign indicates repulsion between atoms. When an atom occupies an empty site, it disrupts the surrounding atoms, leading to an increase in the system’s energy.
Negative Sign: A negative sign suggests attraction between atoms. When an atom occupies an empty site, it stabilizes the surrounding atoms, causing a decrease in the system’s energy.
In summary, a positive ECI suggests repulsion and an unfavorable empty site, while a negative ECI suggests attraction and a favorable empty site for occupation in the context of the Cluster Expansion Method.