We propose a new density functional for the evaluation of the total electronic energy by subtracting the Roothaan energy, i.e. the Hartree energy of the density residual, from the Hohenberg-Kohn-Sham (HKS) functional, which is normally used in self-consistent Kohn-Sham (KS) density functional theory (DFT) calculations. Because of the positive semi-definite nature of the Roothaan energy, the resulting Wang-Zhou (WZ) functional always produces a total energy lower than that from the HKS functional and usually converges to the exact total energy from below. Following the same spirit of the Zhou-Wang-lambda (ZW lambda) functional in the recently proposed orbital-corrected orbital-free (00) DFT method (Zhou and Wang, J Chem Phys 2006,124,081107), we linearly mix the WZ functional with the HKS functional to allow further systematic error cancellations. The resulting Wang-Zhou-alpha (WZ alpha) functional is compared with the ZW lambda functional in OO-DFT calculations for systems within different chemical environment. We find that the optimal value of alpha for the WZ alpha functional is more stable than that of; for the ZW lambda functional. This is because the WZ functional remedies the oscillatory convergence behavior of the Harris functional and renders the direct evaluation of a for the WZ alpha functional more plausible in the application of the linear-scaling OO-DFT method for large systems. (C) 2007 Wiley Periodicals, Inc.

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