Fictitious non-interacting electron

Kohn and Sham provided a further contribution to make the DFT approach useful for practical calculations, by introducing the concept of fictitious non-interacting electrons with the same density as the true interacting electrons [8]. Non-interacting electrons are described by orthonormal single-particle wavefunctions y/i (r) and their density is given by ... 

The first term, 7ks[ ( )]> is the kinetic energy of fictitious, non-interacting electrons and is obtained from the single-electron Kohn Sham equations... 

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