Hylleraas-configuration-interaction Study of the Singlet S Ground State of Neutral Beryllium | NIST

W.S.C. Williams, Carson O. Patterson, A. D. Vira +1 more

Eryn C. Cook, Lucy Lin, Esther Kerns +2 more

Philip R. Johnson, William F. Flynn, D. Blume +2 more

J. Mitroy

The polarizabilities of the three lowest states of the beryllium atom are determined from a large basis configuration interaction calculation. The polarizabilities of the $2{s}^{2}$ ${}^{1}{S}^{e}$ ground state ($37.73$${a}_{0}^{3}$) and the $2s2p$ ${}^{3}{P}_{0}^{o}$ metastable state ($39.04$${a}_{0}^{3}$) are found to be very similar in size and magnitude. This leads to an anomalously small blackbody radiation shift at $300$ K of $\ensuremath{-}$$0.018(4)$ Hz for the $2{s}^{2}$ ${}^{1}{S}^{e}$--$2s2p$ ${}^{3}{P}_{0}^{o}$ clock transition. Magic wavelengths for simultaneous trapping of the ground and metastable states are also computed.

Dae-Soung Kim

Geoffrey W. Hayden, E. J. Melé

We apply the Hubbard-Peierls Hamiltonian to study the low-lying excited states of several model conjugated polymers. The calculations employ a numerical renormalization-group method for chains of intermediate length, and a more approximate truncated configuration-interaction scheme to extrapolate the results to longer systems. In the range of on-site Coulomb repulsion strengths of physical interest, we find that a correlated even-parity singlet excited state competes with the odd-parity singlet excitation expected in the U=0 limit of the model, in agreement with previous studies on the Pariser-Parr-Pople model. The lowest electronic excitations in the model are identified as triplet excitations. Self-consistently-relaxed lattice configurations surrounding these electronic excitations are studied. In addition to the stable photoexcitations predicted in the U=0 limit of the theory, we find that the interelectronic repulsive potential leads to a rich spectrum of competing neutral structures, which are studied and characterized. Coulomb correlations provide a mechanism for production of long-lived spin-1/2 neutral excitations for degenerate ground-state systems, and spin-1 neutral excitations for nondegenerate ground-state systems.