In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method developers and practitioners.

In the current density functional theory of linear and nonlinear time-dependent phenomena, the treatment of exchange and correlation beyond the level of the adiabatic local density approximation is shown to lead to the appearance of viscoelastic stresses in the electron fluid. Complex and frequency-dependent viscosity/elasticity coefficients are microscopically derived and expressed in terms of properties of the homogeneous electron gas. As a first consequence of this formalism, we provide an explicit formula for the linewidths of collective excitations in electronic systems.

Given an expression for the quantum mechanical action $A\left[{\phi }_{j\sigma }\right]$ of an $N$-electron system as a functional of $N$ time-dependent spin orbitals, we present a method of constructing the variationally best local time-dependent single-particle potentials $v_{\sigma }\left(\mathrm{r}t\right)$ which, when inserted in time-dependent single-particle Schrödinger equations for the spin-up and spin-down electrons yield orbitals $\left\{{\phi }_{j\sigma }\right(\mathrm{r}t\left)\right\}$ that make $A\left[{\phi }_{j\sigma }\right]$ stationary. We also propose a simplification of this scheme leading to a time-dependent generalization of the static optimized effective potentials recently introduced by Krieger, Li, and Iafrate [Phys. Lett. A 146, 256 (1990)]