Random-phase approximation, nuclear

In the 1950s, many basic nuclear properties and phenomena were qualitatively understood in terms of single-particle and/or collective degrees of freedom. A hot topic was the study of collective excitations of nuclei such as giant dipole resonance or shape vibrations, and the state-of-the-art method was the nuclear shell model plus random phase approximation (RPA). With improved experimental precision and theoretical ambitions in the 1960s, the nuclear many-body problem was born. The importance of the ground-state correlations for the transition amplitudes to excited states was recognized. 

A simple application of the very general approach used in earlier sections leads to the time-dependent generalization of Hartree-Fock theory. The time-dependent Hartree-Fock (TDHF) equations (Dirac, 1929) were first formulated variationally by Frenkel (1934) they are also widely used in nuclear physics (see e.g. Thouless, 1%1) under the name random-phase approximation (RPA). Since the equations describe response to a perturbation, as in Section 11.9 but now time-dependent, they will... 

The atomic density of the (1 x 1) surface is 1.28 x lO Pt atoms cm [39]. This is approximately 25% lower than the atomic density of the (hex) phase (i.e., 1.61 x lO Pt atoms cm [47]). This density difference results in significant mass transport of platinum atoms during the back-reconstruction. Scanning tunneling microscopy (STM) data demonstrate [47-49] that expelled platinum atoms form clusters with size of 15-25 A. The clusters are randomly distributed within the CO-islands boundaries. Infrared absorption spectroscopy (IRAS) [42,43] and HREELS [31,44,45] have shown the existence of two molecularly adsorbed CO species on the surface of the (1 x 1) islands in bridge (CObr) state and in the on-top (COtop) state. The saturation coverage of CO on the Pt(l 0 0) surface at 300 K, estimated by a nuclear microanalysis, is 0.75 ML [39]. 

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