In this issue of the Advances in Quantum Chemistry, Volume 66, the readers are offered an interesting mix of themes, first an account of the high-Tc mechanism of a recently discovered class of superconductors, with a characteristic alternant lattice structure; a lucid treatise of some of the fundamental core concepts, labeled as conundrums in chemical physics, a state-of-the art description of the electron-dynamics, END, method; and finally new developments regarding unified descriptions of embeddings in both a discrete and a continuum polarizable environment within multiconfigurational self-consistent field (MCSCF) theories. In Chapter 1, the authors review a contemporary hot topic, that is, theories concerning the understanding of a newly discovered class of high-Tc superconductors, that is, the iron-based pnictides and the chalcogenic compounds exhibiting, in analogy with the cuprates previously discovered and discussed, a characteristic alternant lattice structure. Since recent speculations suggest the emergence of superconductivity from repulsive electronic correlations, the authors demonstrate in this review a detailed mechanism for this class of condensates originating in the alternant structure as well as simultaneously exhibiting Yang’s celebrated concept of off-diagonal long-range order, ODLRO. In addition, it is pointed out that the authors proposed conformational stabilization with strong interactions as a possible mechanism for high-temperature superconductivity more than 30 years ago and that a similar repulsive coulomb mechanism for the alternant lattice structure is central to the occurrence of the most stable condensates, exhibiting dx2-y2symmetry for the cuprates and sign alternating s-wave or s±condensate symmetries for the pnictides. In Chapter 2, several fundamental concepts and models that appear challenging to students and teachers in chemistry interrelated scientific disciplines have been presented under the title “Conundrums in Chemical Physics.” In particular, the author provides explanations and validations of concepts such as those of the classical Marcus model and the quantum mechanical Landau theory of electron transfer reactions, or further the semi-classical Landau–Zener approach for diabatic transitions, integrated by the notion of reaction paths as well as the progression of stochastic models, etc. In addition, fundamental mathematical approaches, like the Langevin-, the Fokker–Planck-, and the Klein–Kramers’ equation, are illustrated and evolved. Possible objections of the work presented here concern the connection between Kramers’ account of Transition State theory in the context of phase space diffusion and the irreversible version of the Liouville equation. By transferring the classical concepts to the field of Quantum Chemistry, the author meets the complaints and outlines a time-dependent Liouville superoperator space and Trace Algebra with an emphasis to facilitate the description of the issues facing the developmentof a modern quantum mechanical theory of irreversible processes in analogy with their classical counterparts. Chapter 3 concerns a method for treating molecular dynamics in a nonadiabatic way that treats electrons and nuclei simultaneously. The method, electron nuclear dynamics or END, as presently implemented, reduces the nuclear wavefunction to zero width, making the nuclei act classically, while maintaining Thouless single-determinantal description of the electrons. Typically, the method is implemented in its simplest form and thus has some application problems, as described in this chapter. The chapter deals with the computational simplification of the problem by introducing a density functional (DFT)-based treatment of the electronics in order to include some correlation and yet maintain a single-determinantal description. Chapter 4 in this volume deals with the linear response properties of an electronic state of a system embedded in a polarizable medium. The treatmentis based on an MCSCF theory and leads to the description of the electronic state of an embedded molecule.The content of this volume is quite diverse, and it is hoped that the volume will provide an interesting read for all who have interest in the quantum mechanical description of a wide variety of molecular systems.
Amsterdam: Elsevier, 2013. , 248 p.
Yang's concept of ODLRO, Landau-Zener, electron-nuclear dynamics, electronic states of an embedded molecule