One‐electron properties as variational parameters

The algorithm of Clinton et al. [Phys. Rev. 177, 7 (1969)] for the direct determination of an idempotent density matrix from one-electron expectation values is adapted to perform energy-variational calculations in which the expectation values serve as variational parameters. As an illustration, constrained variational calculations are performed on lithium hydride. A technique is presented to insure that from virtually any idempotent initial guess density matrix, the algorithm will converge to that idempotent density matrix having the desired expectation values which is ’’closest’’ to the initial guess.