title: A quadratic form of the Coulomb operator and an optimization scheme for the extended Kohn-Sham models.
abstract: To construct an optimization scheme for an extension of the Kohn-Sham approach, I introduce an operator form of the Coulomb interaction. This form is the sum of quadratic form pairs, which can be redefined in a self-consistent calculation of a multi-reference density functional theory. A detailed derivation of the form is given. A fluctuation term introduced in the extended Kohn-Sham scheme is expressed in this form for regularization. The present procedure also provides an exact derivation of effective negative interactions in charge fluctuation channels. Relevance to high-temperature superconductors is discussed.
authors.affiliation: Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Kusakabe