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I have been assuming that the gamma point only version of the code uses only one K point and is therefore not very accurate for energies. However, I have noticed people reporting binding energies for molecules on the side walls of carbon nanotubes using a gamma point only calculations. Can someone say a few words about what a gamma point only calculations is and if it can produce reliable energies.

(Non-expert reply: No-one else seems to want to have a go!)

Loosely speaking, Gamma-only treats inter-cell interactions in a non-rigorous way (well, at least some of them). Thus it is good for systems with very large unit cells so that it's the intra-cell interactions that dominate, and for non-periodic systems.

For adsorbates doing Gamma-only calculations will minimise inter-adsorbate interactions, hopefully getting closer to the dilute adsorbate answer. However, it's at the cost of a more approximate description of the substrate. Whether or not this significantly effects the binding energy calculation or not I imagine would have to be assessed on a case-by-case basis (and also depend on the size of the cell used).

Thank you very much ,tjf.

Thank you very much ,tjf.