Density functional theory
(DFT) is a formally exact re-writing of quantum mechanics
with the electron density ρ as the basic variable instead of the wavefunction
. The reduced computational cost of this approach lead to DFT becoming the most popular method of quantum chemistry
from the mid-1990s onwards.
The DFT Difference
The first true density functional theory was developed by Thomas and Fermi in the 1920's.
 P. Hohenberg and W. Kohn, Phys. Rev. 136 (1964) B864.
 W. Kohn and L. J. Sham, Phys. Rev. 140 (1965) A1133.
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