The Nakajima-Zwanzig equation for an operator named for this quantity is the starting point to derive the Redfield equation for that operator named for this quantity. Nesting instabilities can cause waves in this quantity, which can also be caused by the Peierls instability. Screening causes Friedel oscillations in this quantity at twice the Fermi (-5[1])wavevector. The hermitian operator named for this quantity is positive definite and has unit trace, and evolves by the (*) von Neumann (10[1])equation in closed systems. The ground state energy of a system is a functional of only this quantity by the Hohenberg-Kohn (10[1])theorems. Taking the mod square of the wave function gives the ‘probability’ type of this quantity.. For 10 points, name this quantity whose mass type is equal to mass per unit volume. ■END■ (10[1])