Materials properties quantum mechanical methods

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 demands that materials science, fine chemistry, molecular biology, and condensed-matter physics exert on the quantum mechanical methods which have been developed throughout the years for the purpose of calculating the properties of many-particle systems, are really quite formidable. The point is that these disciplines have an exacting need for working methods that lead to... 

The observable properties of solid materials are governed by quantum mechanics, as expressed by solutions of a Schrodinger equation for the motion of the electrons and the nuclei. However, because of the inherent difficulty of obtaining even coarsely approximate solutions of the full many body Schrodinger equation, one t5q)ically focuses on reduced descriptions that are believed to capture the essential energetic of the problem of Interest Tow main quantum mechanics method are Ab initio and density function method (DFT). ... 

There are a number of excellent reviews and discussions about the advances that have taken place in quantum-mechanical method development and their ability to calculate a host of different material properties We therefore, do not go into this in detail in this book. Instead, we present a short overview of covering salient features of the different theoretical and computational methods and their application to catalysis. This is presented in the Appendix along with references to more detailed reviews on the different methods. 

There exists a large body of empirical vulnerability data for conventional EM for which numerous researchers have correlated molecular or material properties [102-156]. Of these, a large number of the molecular properties used in the correlations were predicted using semi-empirical or quantum mechanical methods. While many of these are quite useful in identifying potential vulnerability of an EM, they should not be used to justify mechanistic arguments [157,158]. Additionally, as with all QSPR approaches, the predictive capability is strongly dependent on the quality of the empirical information used in the parameterization. Unreliable empirical information used in the parameterization could result in a highly inaccurate tool. For vulnerability, the majority of the empirical data consists of results of drop-... 

In essence, there are only two types of atomistic computational methodologies which are used for the prediction of materials properties, namely (1) empirical potential (or force field) approaches which describe the interactions between atoms in a quasi-classical form avoiding any details of the electronic structure and (2) quantum mechanical methods which take into account the motions and interactions of the electrons in a material. If the approaches are based solely on fundamental physical constants such as the mass and charge of an electron and no atom-specific parameters are introduced, then the methods are called ab initio or first principles . (In the chemical literature, the term ab initio is sometimes reserved for Hartree-Fock-based methods whereas in solid state physics it typically refers to density functional methods.) Since quantum mechanical methods are not biased towards any particular atom or bonding type, they provide powerful predictive capabilities. On the other hand, the computational effort involved in ab initio methods is several orders of magnitude larger then in the case of empirical potentials. Therefore, both approaches, empirical potential methods and quantum mechanical approaches, have their place. 

Abstract The evaluation of key properties of materials using quantum mechanics (QM) methods is the aim of this chapter. The use of QM is necessary to calculate properties that depend on electron interactions or electron density polarization. Following the Introduction, which covers computational chemistry notions, some basic concepts concerning the Density Functional Theory (DFT) used in the presented calculations are illustrated, in addition to a brief review of intermolecular interactions. The chapter then reviews the assessment of some fundamental quantities, such as the adsorption energies of gases and hydrogen in nano-porous materials and on metallic surfaces, respectively. Finally, the calculation of hydrogen solubilization in metal alloys will be also presented. 

From these early beginnings, computer studies have developed into sophisticated tools for the understanding of defects in solids. There are two principal methods used in routine investigations atomistic simulation and quantum mechanics. In simulation, the properties of a solid are calculated using theories such as classical electrostatics, which are applied to arrays of atoms. On the other hand, the calculation of the properties of a solid via quantum mechanics essentially involves solving the Schrodinger equation for the electrons in the material. 

Calculations using the methods of non-relativistic quantum mechanics have now advanced to the point at which they can provide quantitative predictions of the structure and properties of atoms, their ions, molecules, and solids containing atoms from the first two rows of the Periodical Table. However, there is much evidence that relativistic effects grow in importance with the increase of atomic number, and the competition between relativistic and correlation effects dominates over the properties of materials from the first transition row onwards. This makes it obligatory to use methods based on relativistic quantum mechanics if one wishes to obtain even qualitatively realistic descriptions of the properties of systems containing heavy elements. Many of these dominate in materials being considered as new high-temperature superconductors. 

In this paper, an overview of the origin of second-order nonlinear optical processes in molecular and thin film materials is presented. The tutorial begins with a discussion of the basic physical description of second-order nonlinear optical processes. Simple models are used to describe molecular responses and propagation characteristics of polarization and field components. A brief discussion of quantum mechanical approaches is followed by a discussion of the 2-level model and some structure property relationships are illustrated. The relationships between microscopic and macroscopic nonlinearities in crystals, polymers, and molecular assemblies are discussed. Finally, several of the more common experimental methods for determining nonlinear optical coefficients are reviewed. 

Although RDX strains the limits of accurate applicability of quantum chemistry methods, they have provided valuable information about the decomposition mechanism. Ultimately, it is expected that quantum chemistry will play a vital role in elucidating the elementary reaction mechanisms for energetic materials. In fact, given the experimental difficulties for molecules such as RDX we must look to quantum chemistry. While the quantum chemistry description of the fundamental properties and elementary reactions of RDX is still a work in progress, much has been... 

Design of molecular materials with specific properties often requires interdisciplinary research involving various experimental and theoretical techniques. Molecular modeling by ab initio methods based on quantum-mechanics is now commonly used in such studies. However, theoretical investigations are still dominated by traditional, static approaches in which the stationary points on the respective potential... 

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