Green’s function and density matrices

From wave functions to density functionals via Green s functions and density matrices... 

Hence, in the ground state, a function of one variable is equivalent to a function of N variables This property shows that we have only integrated out explicit information on our way from wave functions via Green s functions and density matrices to densities. Implicitly all the information that was contained in the ground-state wave function is still contained in the ground-state density. Part of the art of practical DFT is how to get this implicit information out, once one has obtained the density ... 

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