XC-functional
One cannot talk about DFT without touching the issue of the exchange-correlation functional. In this video, you will learn what a XC-functional is, how the simplest ones are constructed, and how the hierarchy among XC-functionals looks like.
Now read this Perspective from Science (2002) (you have to go through a free registration first to download the original pdf — an alternative is this link to an image of the pdf) about the search for the “divine” exchange-correlation functional. Part of the text deals with the Jacob’s ladder analogy (optional: a 6-minute oral explanation of this analogy by John Perdew). Now use the forum to explain in your own words what Jacob’s ladder is in the context of DFT :
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optional: digging deeper
The XC-functional is one of those topics one can understand at various levels, from conceptual to (very) technical. The latter is not better than the former, it depends in the first place on what you need this knowledge for. For those of you who want to dig deeper into the topic of exchange-correlation functionals, now or later, a set of optional material is collected here:
- Two Youtube-lectures by C.J. Cramer, about LDA and GGA at a more technical level then discussed above (underneath).
- The 1996 paper from Physical Review Letters by Perdew, Burke and Ernzerhof with the promising title Generalized Gradient Approximation Made Simple, where the PBE functional has been proposed.
- A comprehensive discussion of the 400 XC-functionals that are available in the libxc-library (open access review paper in SoftwareX, 2018, by Lehtola, Steigemann, Oliveira and Marques)
- Nearly 4 hours of pedagogical lectures by John Perdew, covering LDA, GGA, meta-GGA up to the SCAN functional (underneath). The second video in this series deals with the Jacob’s ladder analogy that is discussed also in the paper at the top of this page. (all of these are part of part of a CECAM school on Teaching the Theory in DFT).
The two videos by J.C. Cramer:
compChem.05.05 Density Functional Theory: Local Density Approximation
compChem.05.06 Density Functional Theory: Generalized Gradient Approximation
The four videos by John Perdew :
local density approximation
generalized Gradient Approximation
meta GGA
the SCAN functional
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