title: Derivation of the RPA (Random Phase Approximation) Equation of ATDDFT (Adiabatic Time Dependent Density Functional Ground State Response Theory) from an Excited State Variational Approach Based on the Ground State Functional.
abstract: The random phase approximation (RPA) equation of adiabatic time dependent density functional ground state response theory (ATDDFT) has been used extensively in studies of excited states. It extracts information about excited states from frequency dependent ground state response properties and avoids, thus, in an elegant way, direct Kohn-Sham calculations on excited states in accordance with the status of DFT as a ground state theory. Thus, excitation energies can be found as resonance poles of frequency dependent ground state polarizability from the eigenvalues of the RPA equation. ATDDFT is approximate in that it makes use of a frequency independent energy kernel derived from the ground state functional. It is shown in this study that one can derive the RPA equation of ATDDFT from a purely variational approach in which stationary states above the ground state are located using our constricted variational DFT (CV-DFT) method and the ground state functional. Thus, locating stationary states above the ground state due to one-electron excitations with a ground state functional is completely equivalent to solving the RPA equation of TDDFT employing the same functional. The present study is an extension of a previous work in which we demonstrated the equivalence between ATDDFT and CV-DFT within the Tamm-Dancoff approximation.
authors.affiliation: Department of Chemistry, University of Calgary , University Drive 2500, Calgary Alberta T2N1N4, Canada.
authors.forename: Tom
authors.initials: T
authors.lastname: Ziegler
authors.affiliation: Department of Chemistry, University of Calgary , University Drive 2500, Calgary Alberta T2N1N4, Canada.
authors.forename: Mykhaylo
authors.initials: M
authors.lastname: Krykunov
authors.affiliation: Department of Chemistry, State University of New York . 312 Natural Sciences Complex. Buffalo, New York 14260-3000, United States.
authors.forename: Jochen
authors.initials: J
authors.lastname: Autschbach