Derivation orbital Euler-Lagrange equations

Orbital Euler-Lagrange equations are determined by functional derivatives... 

It is assumed that Ec is so defined that the functional E is minimized for ground states. Ground-state orbital functions and the density function are determined by Euler-Lagrange equations expressed in terms of functional derivatives of E. For any density or orbital functional, with fixed n, infinitesimal orbital variations determine the functional variation... 

As the electronic energy is a function of the nuclear positions as well as function of the orbitals (/ , its derivative is taken with respect to the nuclear positions but also with respect to the wavefunction. The Euler-Lagrange equations then read... 

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