Constrained search in imaginary time

We introduce an imaginary-time evolution method to evaluate the pure-state constrained-search functional from density-functional theory formulated on finite lattices. Simultaneously, it yields a potential that produces a prescribed density of an eigenstate. Besides being a computational scheme, this allows one to gain theoretical insights into the density-potential mapping. The method can be generalized to the optimization of the expectation value of a general self-adjoint operator on a finite-dimensional Hilbert space under a finite number of expectation-value constraints for commuting self-adjoint operators.