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# Harris functional

In computational condensed-matter physics, the Harris energy functional is a non-self-consistent approximation to Kohn-Sham density functional theory.[1] It gives the energy of a combined system as a function of the electronic densities of the isolated parts. The energy of the Harris functional varies much less than the energy of the Kohn-Sham functional as the density moves away from the converged density. Therefore, for many systems the accuracy without the self-consistency may be sufficient. The Harris functional was originally developed for such calculations rather than self-consistent convergence, although it can be applied in a self-consistent manner in which the density is changed. While the Kohn-Sham DFT energy is Variational method (never lower than the ground state energy), the Harris DFT energy was originally believed to be anti-variational (never higher than the ground state energy).[2] This was however conclusively demonstrated to be incorrect.[3][4] Harris functional is used in some codes, such as Fireball[5] and Gaussian.

References

Harris, J. (1985). "Simplified method for calculating the energy of weakly interacting fragments". Physical Review B 31 (4): 1770–1779. Bibcode:1985PhRvB..31.1770H. doi:10.1103/PhysRevB.31.1770.

Zaremba, E. (1990). "Extremal properties of the Harris energy functional". Journal of Physics: Condensed Matter 2 (10): 2479. Bibcode:1990JPCM....2.2479Z. doi:10.1088/0953-8984/2/10/018.

Robertson, I.J.; Farid, B. (1991). "Does the Harris energy functional possess a local maximum at the ground-state density?". Physical Review Letters 66 (25): 3265–3268. Bibcode:1991PhRvL..66.3265R. doi:10.1103/PhysRevLett.66.3265. PMID 10043743.

Farid, B.; Heine, V.; Engel, G.E.; Robertson, I.J. (1993). "Extremal properties of the Harris-Foulkes functional and an improved screening calculation for the electron gas". Physical Review B 48 (16): 11602–11621. Bibcode:1993PhRvB..4811602F. doi:10.1103/PhysRevB.48.11602.

Lewis, James P.; Glaesemann, Kurt R.; Voth, Gregory A.; Fritsch, Jürgen; Demkov, Alexander A.; Ortega, José; Sankey, Otto F. (2001). "Further developments in the local-orbital density-functional-theory tight-binding method". Physical Review B 64 (19): 195103. Bibcode:2001PhRvB..64s5103L. doi:10.1103/PhysRevB.64.195103.

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