The Kadanoff-Baym approach to double excitations in finite systems
Säkkinen, N., Manninen, M., & van Leeuwen, R. (2012). The Kadanoff-Baym approach to double excitations in finite systems. New Journal of Physics, 14 (13032). doi:10.1088/1367-2630/14/1/013032
Published inNew Journal of Physics
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We benchmark many-body perturbation theory by studying neutral, as well as non-neutral, excitations of finite lattice systems. The neutral excitation spectra are obtained by time-propagating the Kadanoff–Baym equations in the Hartree–Fock and the second Born approximations. Our method is equivalent to solving the Bethe–Salpeter equation with a high-level kernel while respecting self-consistency, which guarantees the fulfillment of a frequency sum rule. As a result, we find that a time-local method, such as Hartree–Fock, can give incomplete spectra, while already the second Born approximation, which is the simplest time-non-local approximation, reproduces well most of the additional excitations, which are characterized as double excitations.