Density-orbital embedding theory

In the article density-orbital embedding (DOE) theory is proposed. DOE is based on the concept of density orbital (DO), which is a generalization of the square root of the density for real functions and fractional electron numbers. The basic feature of DOE is the representation of the total supermolecular density ρs as the square of the sum of the DO φa, which represents the active subsystem A and the square root of the frozen density ρf of the environment F. The correct ρs is obtained with φa being negative in the regions in which ρf might exceed ρs. This makes it possible to obtain the correct ρs with a broad range of the input frozen densities ρf so that DOE resolves the problem of the frozen-density admissibility of the current frozen-density embedding theory. The DOE Euler equation for the DO φa is derived with the characteristic embedding potential representing the effect of the environment. The DO square φa2 is determined from the orbitals of the effective Kohn-Sham (KS) system. Self-consistent solution of the corresponding one-electron KS equations yields not only φa2, but also the DO φa itself. © 2010 The American Physical Society.