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Books > Science & Mathematics > Chemistry > Physical chemistry > Quantum & theoretical chemistry
Over the past decade high performance computing has demonstrated the ability to model and predict accurately a wide range of physical properties and phenomena. Many of these have had an important impact in contributing to wealth creation and improving the quality of life through the development of new products and processes with greater efficacy, efficiency or reduced harmful side effects, and in contributing to our ability to understand and describe the world around us. Following a survey ofthe U.K.'s urgent need for a supercomputingfacility for aca demic research (see next chapter), a 256-processor T3D system from Cray Research Inc. went into operation at the University of Edinburgh in the summer of 1994. The High Performance Computing Initiative, HPCI, was established in November 1994 to support and ensure the efficient and effective exploitation of the T3D (and future gen erations of HPC systems) by a number of consortia working in the "frontier" areas of computational research. The Cray T3D, now comprising 512 processors and total of 32 CB memory, represented a very significant increase in computing power, allowing simulations to move forward on a number offronts. The three-fold aims of the HPCI may be summarised as follows; (1) to seek and maintain a world class position incomputational scienceand engineering, (2) to support and promote exploitation of HPC in industry, commerce and business, and (3) to support education and training in HPC and its application.
"A Structural and Vibrational Study of the Chromyl Chlorosulfate,
Fluorosulfate and Nitrate Compounds" presents important studies
related to the structural and vibrational properties on the chromyl
compounds based on Ab-initio calculations. The synthesis and the
study of such properties are of chemical importance because the
stereo-chemistries and reactivities of these compounds are strongly
dependent on the coordination modes that adopt the different
ligands linked to the chromyl group.
"A Structural and Vibrational Investigation into Chromyl Azide,
Acetate, Perchlorate and Thiocyanate Compounds" reviews the
structural and vibrational properties of chromyl azide, acetate,
perchlorate, and thiocyanate from a theoretical point of view by
using Density Functional Theory (DFT) methods. These compounds are
extensively used in organic syntheses and the study of their
structure and spectroscopy has become fundamental.
A summary of all the most important aspects of supramolecular science, from molecular recognition in chemical and biological systems to supramolecular devices, materials and catalysis. The 17 chapters cover calixarenes, catenanes, cavitands, cholophanes, dendrimers, membranes and self-assembly systems, molecular modelling, molecular level devices, organic materials, peptides and protein surfaces, recognition of carbohydrates, rotaxanes, supramolecular catalysis. A forward-looking chapter written by J.-M. Lehn indicated the future prospects for the entire field. Audience: Ph.D. students and young researchers in chemistry, physics and biology.
From the beginnings of modern chemistry, molecular structure has been a lively area of research and speculation. For more than half a century spectroscopy and other methods have been available to characterize the structures and shapes of molecules, particularly those that are rigid. However, most molecules are at least to some degree non-rigid and this non-rigidity plays an important role in such diverse areas as biological activity, energy transfer, and chemical reactivity. In addition, the large-amplitude vibrations present in non-rigid molecules give rise to unusual low-energy vibrational level patterns which have a dramatic effect on the thermodynamic properties of these systems. Only in recent years has a coherent picture of the energetics and dynamics of the conformational changes inherent in non-rigid (and semi-rigid) molecules begun to emerge. Advances have been made in a number of different experimental areas: vibrational (infrared and Raman) spectroscopy, rotational (microwave) spectroscopy, electron diffraction, and, most recently, laser techniques probing both the ground and excited electronic states. Theoretically, the proliferation of powerful computers coupled with scientific insight has allowed both empirical and ab initio methods to increase our understanding of the forces responsible for the structures and energies of non-rigid systems. The development of theory (group theoretical methods and potential energy surfaces) to understand the unique characteristics of the spectra of these floppy molecules has also been necessary to reach our present level of understanding. The thirty chapters in this volume contributed by the key speakers at the Workshop are divided over the various areas. Both vibrational and rotational spectroscopy have been effective at determining the potential energy surfaces for non-rigid molecules, often in a complementary manner. Recent laser fluorescence work has extended these types of studies to electronic excited states. Electronic diffraction methods provide radial distribution functions from which both molecular structures and compositions of conformational mixtures can be found. Ab initio calculations have progressed substantially over the past few years, and, when carried out at a sufficiently high level, can accurately reproduce (or predict ahead of time) experimental findings. Much of the controversy of the ARW related to the question of when an ab initio is reliable. Since the computer programs are readily available, many poor calculations have been carried out. However, excellent results can be obtained from computations when properly done. A similar situation exists for experimental analyses. The complexities of non-rigid molecules are many, but major strides have been taken to understand their structures and conformational processes.
The ideas of probability are all around us. Lotteries, casino gambling, the al most non-stop polling which seems to mold public policy more and more these are a few of the areas where principles of probability impinge in a direct way on the lives and fortunes of the general public. At a more re moved level there is modern science which uses probability and its offshoots like statistics and the theory of random processes to build mathematical descriptions of the real world. In fact, twentieth-century physics, in embrac ing quantum mechanics, has a world view that is at its core probabilistic in nature, contrary to the deterministic one of classical physics. In addition to all this muscular evidence of the importance of probability ideas it should also be said that probability can be lots of fun. It is a subject where you can start thinking about amusing, interesting, and often difficult problems with very little mathematical background. In this book, I wanted to introduce a reader with at least a fairly decent mathematical background in elementary algebra to this world of probabil ity, to the way of thinking typical of probability, and the kinds of problems to which probability can be applied. I have used examples from a wide variety of fields to motivate the discussion of concepts."
Both molecular spectroscopy and computational chemistry have witnessed rapid significant progresses in recent years. On the one hand, it is nowadays possible to compute, to quite a reasonable degree of accuracy, almost all fundamental spectroscopic properties for small molecular systems. The theoretical approach is now properly considered to be of fundamental importance in attaining a high degree of understanding of spectroscopic information. Moreover, it may be also a great help in designing and planning experiments. On the other hand, new and very powerful experimental techniques have been developed. This book combines an advanced teaching standpoint with an emphasis on the interplay between theoretical and experimental molecular spectroscopy. It covers a wide range of topics (such as molecular dynamics and reactivity, conformational analysis, hydrogen bonding and solvent effects, spectroscopy of excited states, complex spectra interpretation and simulation, software development and biochemical applications of molecular spectroscopy) and considers a large variety of molecular spectroscopic techniques, either from an experimental or from a theoretical perspective. (short text) This book combines an advanced teaching standpoint with an emphasis on the interplay between theoretical and experimental molecular spectroscopy. It covers a wide range of topics (such as molecular dynamics and reactivity, conformational analysis, hydrogen bonding and solvent effects, spectroscopy of excited states, complex spectra interpretation and simulation, software development and biochemical applications of molecular spectroscopy) and considers a large variety of molecular spectroscopic techniques either from an experimental or from a theoretical perspective.
The theoretical chemist is accustomed to judging the success of a theoretical prediction according to how well it agrees with an experimental measurement. Since the object of theory is the prediction of the results of experiment, that would appear to be an entirely satisfactory state ofaffairs. However, ifit is true that "the underlying physicallaws ...for the whole ofchemistryare ...completely known" (1), thenit shouldbepossible,atleastinprinciple, topredict theresults of experiment moreaccurately than they canbe measured. Ifthe theoreticalchemist could obtain exact solutions ofthe Schrodinger equation for many-body systems, then the experimental chemist would soon become accustomed to judging the success ofan experimental measurement by how well it agrees with a theoretical prediction. In fact, it is now possible to obtainexact solutions ofthe Schrodinger equation for systems ofa few electrons(2-8). These systems include the molecular ion Ht, the molecule H , the reaction intermediate H-H-H, the unstable pair H-He, the 2 stable dimer He2' and the trimer He3. The quantum Monte Carlo method used in solving the time-independent Schrodinger equation for these systems is exact in that it requires no physical or mathematical assumptions beyond those of the Schrodinger equation. As in most Monte Carlo methods there is a statistical or sampling error which is readily estimated.
"Kinetics and Dynamics" on molecular modeling of dynamic processes opens with an introductory overview before discussing approaches to reactivity of small systems in the gas phase. Then it examines studies of systems of increasing complexity up to the dynamics of DNA. This title has interdisciplinary character presenting wherever possible an interplay between the theory and the experiment. It provides basic information as well as the details of theory and examples of its application to experimentalists and theoreticians interested in modeling of dynamic processes in chemical and biochemical systems. All contributing authors are renowned experts in their fields and topics covered in this volume represent the forefront of today's science.
Density Functional Theory (DFT) has firmly established itself as the workhorse for atomic-level simulations of condensed phases, pure or composite materials and quantum chemical systems. This work offers a rigorous and detailed introduction to the foundations of this theory, up to and including such advanced topics as orbital-dependent functionals as well as both time-dependent and relativistic DFT. Given the many ramifications of contemporary DFT, the text concentrates on the self-contained presentation of the basics of the most widely used DFT variants: this implies a thorough discussion of the corresponding existence theorems and effective single particle equations, as well as of key approximations utilized in implementations. The formal results are complemented by selected quantitative results, which primarily aim at illustrating the strengths and weaknesses of particular approaches or functionals. The structure and content of this book allow a tutorial and modular self-study approach: the reader will find that all concepts of many-body theory which are indispensable for the discussion of DFT - such as the single-particle Green's function or response functions - are introduced step by step, along with the actual DFT material. The same applies to basic notions of solid state theory, such as the Fermi surface of inhomogeneous, interacting systems. In fact, even the language of second quantization is introduced systematically in an Appendix for readers without formal training in many-body theory.
This book introduces the concept of crystallographic non- rigidity and asymmetry of the transition elements as central atoms organometallic compounds. This intrinsic behavior of central atoms in condensed matter is quantified by applying statistical approach. Averaging of extrinsic factors in crystal structures is tested by using variance analysis. Introductionof the above mentioned concept and applications of variance analysis as an approximation for considering factors influencing properties of central atomin the crystal is original and new.
The Sixth International Conference on Miniaturized Chemical and Biochemical Analysis Systems, known as IlTAS2002, will be fully dedicated to the latest scientific and technological developments in the field of miniaturized devices and systems for realizing not only chemical and biochemical analysis but also synthesis. The first IlTAS meeting was held in Enschede in 1994 with approximately 160 participants, bringing together the scientists with background in analytical and biochemistry with those with Micro Electro Mechanical Systems (MEMS) in one workshop. We are grateful to Piet Bergveld and Albert van den Berg of MESA Research Institute of the University of Twente for their great efforts to arrange this exciting first meeting. The policy of the meeting was succeeded by late Prof. Dr. Michael Widmer in the second meeting, IlTAS'96 held in Basel with 275 participants. The first two meetings were held as informal workshops. From the third workshop, IlTAS'98 (420 participants) held in Banff, the workshop had become a worldwide conference. Participants continued to increase in IlTAS2000 (about 500 participants) held in Enschede and IlTAS2001 (about 700 participants) held in Monterey. The number of submitted papers also dramatically increased in this period from 130 in 1998, 230 in 2000 to nearly 400 in 2001. From 2001, IlTAS became an annual symposium. The steering committee meeting held in Monterey, confirmed the policy of former IlTAS that quality rather than quantity would be the key-point and that the parallel-session format throughout the 3.
The state-of-the-art in contemporary theoretical chemistry is presented in this 4-volume set with numerous contributions from the most highly regarded experts in their field. It provides a concise introduction and critical evaluation of theoretical approaches in relation to experimental evidence.
Structure, Bonding, and Reactivity of Reactant Complexes and Key Intermediates, by Elena Soriano and Jose Marco-Contelles.- Cycloisomerization of 1, "n"-Enynes Via Carbophilic Activation, by Patrick Yves Toullec and Veronique Michelet.-
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Criteria of orbital symmetry conservation had a profound influence on mechanistic thinking in organic chemistry and are still commonly applied today. The author presents a coherent set of operational rules for the analysis of scope and reliability. It is written from the viewpoint of Orbital Correspondence Analysis in Maximum Symmetry (OCAMS). Its advantage lies in its provision of a coherent overview of the relation between symmetry and mechanism. For reasons of consistency, the book remains within the framework of molecular orbital theory.
During the last twenty years, the multiplicity of potential carbon structures has consistently posed a formidable challenge to theoretical and computational physicists. Several different methods are currently being used to study the structure and the properties of such systems. These methods include simulations based on empirical potentials, tight-binding calculations and density functional theory (DFT). A combination of these methods is needed to make significant progress in the carbon field. This volume provides the reader with a survey of state-of-the-art theoretical and computational contributions featuring novel carbon systems (excluding nanotubes). The chapters are authored by leading researchers who are all actively involved with different aspects of carbon structure and property elucidation. Consequently, a variety of methods are presented to the reader. The editors have successfully compiled an informative book that: Showcases the latest results in carbon materials "Computer-Based Modeling of Novel Carbon Systems and Their Properties" is aimed at advanced undergraduates, graduates, and researchers with an interest in computational nanomaterials."
The focus of this thesis is the computational modelling of transition metal bimetallic (nanoalloy) clusters. More specifically, the study of Pd-Pt, Ag-Pt, Au-Au and Pd-Au as a few tens of atoms in the gas phase. The author used a combination of global optimization techniques - coupled with a Gupta-type empirical many-body potential - and Density Functional Theory (DFT) calculations to study the structures, bonding and chemical ordering, as well as investigate the chemisorptions of hydrogen and carbon monoxide on bimetallic clusters. This research is highly relevant to experimental catalytic studies and has resulted in more than seven publications in international journals.
This text is designed as a practical introduction to quantum chemistry. Quantum chemistry is applied to explain and predict molecular spectroscopy and the electronic structure of atoms and molecules. In addition, the text provides a practical guide to using molecular mechanics and electronic structure computations including ab initio, semi-empirical, and density functional methods. The use of electronic structure computations is a timely subject as its applications in both theoretical and experimental chemical research is increasingly prevalent. This text is written in a format that fosters mastery of the subject both in competency in the mathematics and in obtaining a conceptual understanding of quantum mechanics. The chemistry student's interest is maintained early on in the text where quantum mechanics is developed by applying it to molecular spectroscopy and through conceptual questions labeled as Chemical Connection. Questions throughout the text labeled as Chemical Connection and Points of Further Understanding focus on conceptual understanding and consequences of quantum mechanics.If an Instructor chooses, these questions can be used as a basis for classroom discussion encouraging cooperative learning techniques. This text provides a solid foundation from which students can readily build further knowledge of quantum chemistry in more advanced courses. In cases where this is a final course in quantum chemistry, this text provides the student not only with an appreciation of the importance of quantum mechanics to chemistry, but also with a practical guide to using electronic structure computations.
Kinetic Monte Carlo (kMC) simulations still represent a quite new area of research, with a rapidly growing number of publications. Broadly speaking, kMC can be applied to any system describable as a set of minima of a potential-energy surface, the evolution of which will then be regarded as hops from one minimum to a neighboring one. The hops in kMC are modeled as stochastic processes and the algorithms use random numbers to determine at which times the hops occur and to which neighboring minimum they go. Sometimes this approach is also called dynamic MC or Stochastic Simulation Algorithm, in particular when it is applied to solving macroscopic rate equations. This book has two objectives. First, it is a primer on the kMC method (predominantly using the lattice-gas model) and thus much of the book will also be useful for applications other than to surface reactions. Second, it is intended to teach the reader what can be learned from kMC simulations of surface reaction kinetics. With these goals in mind, the present text is conceived as a self-contained introduction for students and non-specialist researchers alike who are interested in entering the field and learning about the topic from scratch.
"Relativistic Methods for Chemists," written by a highly qualified team of authors, is targeted at both experimentalists and theoreticians interested in the area of relativistic effects in atomic and molecular systems and processes and in their consequences for the interpretation of the heavy element's chemistry. The theoretical part of the book focuses on the relativistic methods for molecular calculations discussing relativistic two-component theory, density functional theory, pseudopotentials and correlations. The experimentally oriented chapters describe the use of relativistic methods in different applications focusing on the design of new materials based on heavy element compounds, the role of the spin-orbit coupling in photochemistry and photobiology, and chirality and its relations to relativistic description of matter and radiation. This book is written at an intermediate level in order to appeal to a broader audience than just experts working in the field of relativistic theory.
Nonlinear dynamics is now recognized as playing a crucial role in a wide variety of disciplines. But what is only just beginning is the important process of cross fertilization and transfer of knowledge and expertise from one area to another. This book is intended to promote this process which will undoubtedly contribute greatly to furthering our understanding of complex systems. Contributions are provided by leading experts from the areas of sociology, cognitive science, chemistry, physiology, ecology, economics, neural networks and physics.
Stochastic Energetics by now commonly designates the emerging field that bridges the gap between stochastic dynamical processes and thermodynamics. Triggered by the vast improvements in spatio-temporal resolution in nanotechnology, stochastic energetics develops a framework for quantifying individual realizations of a stochastic process on the mesoscopic scale of thermal fluctuations. This is needed to answer such novel questions as: Can one cool a drop of water by agitating an immersed nano-particle? How does heat flow if a Brownian particle pulls a polymer chain? Can one measure the free-energy of a system through a single realization of the associated stochastic process? This book will take the reader gradually from the basics to the applications: Part I provides the necessary background from stochastic dynamics (Langevin, master equation), Part II introduces how stochastic energetics describes such basic notions as heat and work on the mesoscopic scale, Part III details several applications, such as control and detection processes, as well as free-energy transducers. It aims in particular at researchers and graduate students working in the fields of nanoscience and technology.
Spiro Quantum Chemistry is a popular as well as technical presentation of the ideas surrounding the emergence of a synthetic, analytical, and theoretical spiro quantum chemistry edifice, as well as a chemical topology scheme that successfully describes molecules and patterns, including the hydrocarbons and allotropes of carbon. In particular, the purpose of this book is to describe the generalization and realization of the organic chemistry concept of spiroconjugation into 1-, 2- and 3-dimensions. The book is divided into three parts: The first part describes spiroconjugation and presents a C lattice that exhibits the spiroconjugation phenomena in fully 3-dimensions. It also described the corresponding 1-dimensional substructures of this lattice that exhibit spiroconjugation delocalized in 1-D. The second part presents experimental evidence for the synthetic realization of this so-called glitter allotrope of C that is spiroconjugated in 3-D, and present evidence why this synthetically realized C allotrope has a metallic status. The third part describes the chemical topology of the glitter C allotrope and of the other commonly known allotropes of C.This chemical topology enables one to map the C allotropes, including glitter, in a topology space allowing one to classify them. This unique book provides insights into the potential richness of organic chemistry in terms of a source of a metallic allotrope of C. The reader will learn to appreciate the generalization of the spiroconjugation phenomenon in 1-D, 2-D, and 3D as a concept in organic chemistry.
There are both a remote and a proximate history in the development of this book. We would like to acknowledge first the perceptiveness of the technical administrators at RCA Laboratories, Inc. during the 1970s, and in particular Dr. P. N. Yocom. Buoyed up by the financial importance of yttrium oxysulfide: europium as the red phosphor of color television tubes, they allowed us almost a decade of close cooperation aimed at understanding the performance of this phosphor. It is significant that we shared an approach to research in an industrial laboratory which allowed us to avoid the lure of "first-principles" approaches (which would have been severely premature) and freed us to formulate and to study the important issues directly. We searched for a semiquantitative understanding of the properties observed in luminescence, i. e., where energy absorption occurs, where emission occurs, and with what efficiency this conversion process takes place. We were aware that the nonradi ative transition rates found in practice vary enormously with temperature and, for a given activator, with small changes in its environment. We traced the source of this enormous variation to the magnitude of the vibrational overlap integrals, which have strong dependences on the rearrangements occurring during optical transitions and on the vibrational number of the initial electronic state. We were willing to excise from the problem the electronic aspects - the electronic wavefunctions' and their transition integrals -by treating them as parameters to be obtained from the experimental data."
The study of molecular collisions at energies from less than about 100 eV 3 down to a few 10- eV, which is roughly the range of chemical interest, has greatly expanded in the last 10 to 20 years. As in many fields, this activity has been stimulated by parallel advances in theory which have triggered the autocatalytic positive feedback system of experiment challenging theory and vice versa. Possibly the biggest driving force, however, has been the growing awareness that molecular collisions are important in our understanding of na tural and man-made environments. Molecular collision dynamics is now studied in connection with molecular formation in interplanetary space, upper atmo sphere chemistry, plasmas, lasers and fusion reactors, and is crucial for understanding gas-dynamic flow processes, gas-phase chemical reactions and catalysis. Despite the great strides made in studying elementary collisions in laboratory scattering experiments, many of the processes in these areas are too complicated for us to hope ever to study them in detail in the labo ratory. Thus in the long run we shall have to rely on theory. Initially, I think many of us, like myself, had hoped that the development of fast compu ters would outpace the demands on computing time so that "brute force" quan tum-mechanical exact calculations would provide all the answers. Unfortunate ly this has not been the case and efficient approximations are needed. They can be broadly classified as classical, semiclassical or semiquantal." |
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