Quantum molecular dynamic materials

Quantum Molecular Dynamic Simulation of Proton Conducting Materials... 

In this chapter we will review the recent developments in simulating and modelling proton transport. We will put a special emphasis on studies employing classical and quantum molecular-dynamics simulations, but also include basic studies that have focussed on model systems using accurate quantum-chemical methods. Proton-transport and dilfusion phenomena in liquids - such as water, inorganic acids, or organic liquids - will be discussed as well as in biomolecules, solid-state materials, and at the solid-liquid interface. Many of these materials are used in proton-transporting fuel-cell membranes, so that membrane materials will be the focus of the last section. 

Sect. 2.3.2, these long time scales can range from fj,s to hours. These time scales are clearly beyond the reach of any classical or quantum molecular dynamics approach. Several methods have been proposed over the years to overcome this difficulty. Here we limit our discussion to a couple of them, since they are by far the most successful and widely applied ones in the field of disordered materials and condensed phases. 

All the macroscopic properties of polymers depend on a number of different factors prominent among them are the chemical structures as well as the arrangement of the macromolecules in a dense packing [1-6]. The relationships between the microscopic details and the macroscopic properties are the topics of interest here. In principle, computer simulation is a universal tool for deriving the macroscopic properties of materials from the microscopic input [7-14]. Starting from the chemical structure, quantum mechanical methods and spectroscopic information yield effective potentials that are used in Monte Carlo (MC) and molecular dynamics (MD) simulations in order to study the structure and dynamics of these materials on the relevant length scales and time scales, and to characterize the resulting thermal and mechanical proper-... 

The first topic has an important role in the interpretation and calculation of atomic and molecular structures and properties. It is needless to stress the importance of electronic correlation effects, a central topic of research in quantum chemistry. The relativistic formulations are of great importance not only from a formal viewpoint, but also for the increasing number of studies on atoms with high Z values in molecules and materials. Valence theory deserves special attention since it improves the electronic description of molecular systems and reactions with the point of view used by most laboratory chemists. Nuclear motion constitutes a broad research field of great importance to account for the internal molecular dynamics and spectroscopic properties. 

The credit load for die computational chemistry laboratory course requires that the average student should be able to complete almost all of the work required for the course within die time constraint of one four-hour laboratory period per week. This constraint limits the material covered in the course. Four principal computational methods have been identified as being of primary importance in the practice of chemistry and thus in the education of chemistry students (1) Monte Carlo Methods, (2) Molecular Mechanics Methods, (3) Molecular Dynamics Simulations, and (4) Quantum Chemical Calculations. Clearly, other important topics could be added when time permits. These four methods are developed as separate units, in each case beginning with die fundamental principles including simple programming and visualization, and building to the sophisticated application of the technique to a chemical problem. 

The research of Paul Brumer and his colleagues addresses several fundamental problems in theoretical chemical physics. These include studies of the control of molecular dynamics with lasers.98 In particular, the group has demonstrated that quantum interference effects can be used to control the motion of molecules, opening up a vast new area of research. For example, one can alter the rate and yield of production of desirable molecules in chemical reactions, alter the direction of motion of electrons in semiconductors, and change the refractive indices of materials etc. by creating and manipulating quantum interferences. In essence, this approach, called coherent control, provides a method for manipulating chemistry at its most fundamental level.99... 

T. A. Kavassalis, Phys. Can., 51, 92 (1995). The Application of Quantum Mechanics and Molecular Dynamics to the Design of New Materials in an Industrial Laboratory. 

The development of multiscale simulation techniques that involve the atomistic modeling of various structures and processes still remains at its early stage. There are many problems to be solved associated with more accurate and detailed description of these structures and processes. These problems include the development of efficient and fast methods for quantum calculations at the atomistic level, the development of transferable interatomic potentials (especially, reactive potentials) for molecular dynamic simulations, and the development of strategies for the application of multiscale simulation methods to other important processes and materials (optical, magnetic, sensing, etc.). 

Nevertheless, ab initio or semiempirical quantum chemical calculations, with clusters to represent the catalytic solid material, can help build up a model of the catalytic system and study effects of modifications [52], Even simulation of the molecular dynamics of the interaction between reactants or intermediates, together with replication of the unit cell of the catalytic solid in a simple force field, may describe observed effects in a catalytic system and may be able to predict the effect of catalyst modifications [53]. 

Progress was also reported in modeling the reaction and transportation processes on fuel cell catalysts and through membranes, using multiple paradigms as well as starting from first principle quantum mechanics to train a reactive force field that can be applied for large scale molecular dynamics simulations. It is expected that the model would enable the conception, synthesis, fabrication, characterization, and development of advanced materials and structures for fuel cells . 

Two conflicting needs appear when working in the field of quantum chemistry. On one hand, the extreme need for high precision calculations, which certainly implies the need for better and more complex wavefunctions needed for the design of new materials with specific characteristics. On the other hand, the need for conceptual interpretations, which will allow for the development of physical and chemical intuition. The development of this intuition is certainly difficult if the wavefunctions are too complex. Since this review is oriented toward the uses of precise first principles methods complementing molecular dynamics simulations, we are focusing on how the development of precise methods helps to improve our understanding and... 

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