Hello, I am a 3rd year chemistry student and I'm writing my project report on computational chemistry. does anyone know how PBEsol improves upon the PBE functional?
Thanks in advance
Both the PBE and PBEsol are first-principles generalized gradient approximations (GGAs). A simple modification of PBE is the PBEsol functional, which differs from PBE only in two parameters, and is designed to improve upon PBE for equilibrium properties of bulk solids and their surfaces. The main difference between them is that they are based upon different selections of exact constraints to satisfy.
At the GGA level, but not at the higher meta-GGA level [Meta-GGA DFT functional in its original form includes the second derivative of the electron density (the Laplacian), whereas GGA includes only the density and its first derivative in the exchange-correlation potential], one can at most satisfy two out of the following three constraints exactly:
1. second-order gradient expansion for exchange.
2. second-order gradient expansion for correlation
3. the local spin density (LSD)-like linear density response of a uniform electron gas.
The PBE satisfies numbers 2 and 3 but not 1, whereas the PBEsol satisfies number 1 and compromises between numbers 2 and 3.
From the performance perspective, the PBEsol describes more correctly the stereoelectronic (SE) effects in many hydrocarbons than many other DFT functional approximations, applies to densely packed solids, and is also useful for large organic molecules (in the absence of free atoms).
On the other hand, although no GGA without a dispersion correction can account for long-range correlation, the PBEsol (after the error cancelation between exchange and correlation) can apparently account for medium-range interaction better than the PBE.
I hope you found this useful!
Hey thank you soo much Seyedeh Tahereh Hosseini, i really appreciate it!
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