Quantum critical phenomena

QUANTUM CRITICAL PHENOMENA AND THE ANOMALOUS LOW-TEMPERATURE PROPERTIES OF THE U(Pt,Pd)3 SYSTEM... 

Abstract Recently, quantum critical phenomena related to a pressure induced loss... 

Keywords quantum critical phenomena, heavy-fermion compound, U(Pt,Pd)3 system... 

Quantum critical phenomena and the anomalous low-temperature properties... 131... 

The field of quantum critical phenomena in atomic and molecular physics is still in its infancy and there are many open questions about the interpretations of the results, including whether or not these quantum phase transitions really do exist. The possibility of exploring these phenomena experimentally in the... 

In any particular situation, it is usually possible to give a variety of reasons why the observed quantity behaves in an erratic manner. The observed quantity may be critically dependent on certain parameters and the observed fluctuations attributed to slight variations of these parameters. The implication here is that the observed fluctuations appear erratic only because we have not taken the trouble to make a sufficiently precise analysis of the situation to disclose the pattern the observations are following. It is also possible, in some situations, to adopt the viewpoint that certain aspects of the phenomenon being studied are inherently unknowable and that the best physical laws we can devise to explain the phenomenon will have some form of randomness or unpredictability built into them. Such is the case, for example, with thermal noise voltages, which are believed to be governed by the probabilistic laws of quantum physics. 

Transition state theory, as embodied in Eq. 10.3, or implicitly in Arrhenius theory, is inherently semiclassical. Quantum mechanics plays a role only in consideration of the quantized nature of molecular vibrations, etc., in a statistical fashion. But, a critical assumption is that only those molecules with energies exceeding that of the transition state barrier may undergo reaction. In reality, however, the quantum nature of the nuclei themselves permits reaction by some fraction of molecules possessing less than the energy required to surmount the barrier. This phenomenon forms the basis for QMT. ... 

The concepts of hybridisation and resonance are the cornerstones of VB theory. Unfortunately, they are often misunderstood and have consequently suffered from much unjust criticism. Hybridisation is not a phenomenon, nor a physical process. It is essentially a mathematical manipulation of atomic wave functions which is often necessary if we are to describe electron-pair bonds in terms of orbital overlap. This manipulation is justified by a theorem of quantum mechanics which states that, given a set of n respectable wave functions for a chemical system which turn out to be inconvenient or unsuitable, it is permissible to transform these into a new set of n functions which are linear combinations of the old ones, subject to the constraint that the functions are all mutually orthogonal, i.e. the overlap integral J p/ip dT between any pair of functions ip, and op, (i = j) is always zero. This theorem is exploited in a great many theoretical arguments it forms the basis for the construction of molecular orbitals as linear combinations of atomic orbitals (see below and Section 7.1). 

The basic concept of the existence of a critical temperature for the onset of macroscopic occupation of a single quantum ground state of a boson system is applicable both for liquid He and for weakly interacting low-density atomic vapors. The phenomenon of Bose-Einstein condensation is not limited to an ideal Bose gas and prevails also in a strongly interacting boson system. The bridging between Bose-Einstein condensation in the low-density, weak... 

Abstract The Vibrational Circular Dichroism (VCD) spectroscopy has been developing rapidly in both experimental and theoretical aspects. Currently, the VCD has become one of the most effective and reliable spectroscopic technique to determine the absolute configuration of chiral molecules. Its success is related to the availability of instrumentation and software for quantum-chemical calculation of the spectra. Nowadays, large parts of the VCD spectra can be trustfully predicted by theory and critically verified by confiding experiment, and vice versa. In the last decade, several theoretical and experimental VCD studies reported on VCD chirality transfer phenomenon occurring when an achiral molecule becomes VCD active as a result of intermolecular interactions with a chiral one. There are still some theoretical and experimental uncertainties about the VCD chirality transfer, however, benefits from an comprehensive use of the phenomenon can push our ability to diversify the intermolecular complexes and deepen our understanding of intermolecular interactions. This chapter is a review of the computational studies on VCD chirality transfer phenomenon supported by the experimental references, and ended by perspectives. 

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