H2H_2 and (H2)2(H_2)_2 molecules with an ab initio optimization of wave functions in correlated state: Electron-proton couplings and intermolecular microscopic parameters

The hydrogen molecules $H_2$ and $(H_2)_2$ are analyzed with electronic correlations taken into account between the $1s$ electrons exactly. The optimal single-particle Slater orbitals are evaluated in the correlated state of $H_2$ by combining their variational determination with the diagonalization of the full Hamiltonian in the second-quantization language. All electron--ion coupling constants are determined explicitly and their relative importance is discussed. Sizable zero-point motion amplitude and the corresponding energy are then evaluated by taking into account the anharmonic contributions up to the ninth order in the relative displacement of the ions from their static equilibrium value. The applicability of the model to the solid molecular hydrogen is briefly analyzed by calculating intermolecular microscopic parameters for $2 \times H_2$ rectangular configurations.Comment: 14 pages, 14 figures, 6 table

Renormalized spin waves in the AF Heisenberg-Kondo model for heavy fermions.

Recent neutron measurements in CeIn_3 and CePd_2Si_3 evidenced spin wave excitations at low temperatures. These heavy fermion compounds exhibit AF long range order, but a strong competition between the RKKY interaction and Kondo effect is evidenced by their nearly equal N?el and Kondo temperatures. Our aim is to show how magnons in the AF phase of these compounds can be dexribed by a microscopic Heisenberg-Kondo model [J. Iglesias et al. PRB 56, 11820 (1997)] introduced before for the non-magnetic phase. The model includes the correlated Ce 4f electrons hybridized with the conduction band, and we consider competing RKKY and Kondo AF couplings. Carrying on a series of unitary transformations we perturbatively derive an effective Hamiltonian which, projected onto the AF electron ground state, describes the spin wave excitations, renormalized by their interaction with the correlated itinerant electrons. We numerically study how the different parameters of the model influence the renormalization of the magnons and compare our results with available experimental data, finding good agreement with the spin wave measurements in cubic CeIn_