Gateaux functional derivative

This defines a Gateaux functional derivative [26, 102], whose value depends on a direction in the function space, reducing to a Frechet derivative only if all e, are equal. Defining Tt = t + v, an explicit orbital index is not needed if Eq. (5.10) is interpreted to define a linear operator acting on orbital wave functions, TL — v = t. The elementary chain rule is valid when the functional... 

In the noninteracting problem both required functional derivatives can be evaluated from explicit orbital functional derivatives. In detail, fAp- = itiyflh and = . For variations of the partial densities pl = 4> 4>i, this implies Gateaux functional derivatives [26,102] = ihyfii and = tfa. The implied or-... 

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