Orbital functional theory of linear response and excitation

Orbital functional theory (OFT) is based on a rule that determines a single-determinant reference state Φ for any exact N-electron eigenstate ψ. An OFT model postulates an explicit correlation energy functional Ec of occupied orbital functions {φi} and occupation numbers {ni}. The orbital Euler-Lagrange equations are analogous to Kohn-Sham equations, but do not in general contain local potential functions. Time-dependent Hartree-Fock theory is generalized in OFT to a formally exact linear response theory that includes electronic correlation. In the exchange-only limit, the theory reduces to the random-phase approximation of many-body theory. The formalism determines excitation energies. © 2002 John Wiley & Sons, Inc. Int. J. Quantum. Chem.