Wai-Kee Li, Gong-Du Zhou, and Thomas Chung Wai Mak
- Published in print:
- 2008
- Published Online:
- May 2008
- ISBN:
- 9780199216949
- eISBN:
- 9780191711992
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199216949.003.0005
- Subject:
- Physics, Crystallography: Physics
This chapter first discusses the difference between semi-empirical and ab initio methods, then devotes most of the remaining pages to ab initio calculations. Each ab initio calculation is defined by ...
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This chapter first discusses the difference between semi-empirical and ab initio methods, then devotes most of the remaining pages to ab initio calculations. Each ab initio calculation is defined by two ‘parameters’: the basis set employed and the level of electron correlation adopted. These two topics are discussed in some detail. Density functional theory is also discussed, which has gained popularity in recent years. After describing these computational methods, a brief assessment on the performance of various levels of theory in yielding structural parameters, vibrational frequencies, and energetic quantities is given. Finally, a few examples are selected from recent literature to show how computations complement experiments to arrive at meaningful conclusions.Less
This chapter first discusses the difference between semi-empirical and ab initio methods, then devotes most of the remaining pages to ab initio calculations. Each ab initio calculation is defined by two ‘parameters’: the basis set employed and the level of electron correlation adopted. These two topics are discussed in some detail. Density functional theory is also discussed, which has gained popularity in recent years. After describing these computational methods, a brief assessment on the performance of various levels of theory in yielding structural parameters, vibrational frequencies, and energetic quantities is given. Finally, a few examples are selected from recent literature to show how computations complement experiments to arrive at meaningful conclusions.
Ted Janssen, Gervais Chapuis, and Marc de Boissieu
- Published in print:
- 2018
- Published Online:
- August 2018
- ISBN:
- 9780198824442
- eISBN:
- 9780191863288
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780198824442.003.0004
- Subject:
- Physics, Crystallography: Physics, Condensed Matter Physics / Materials
This chapter discusses the X-ray and neutron diffraction methods used to study the atomic structures of aperiodic crystals, addressing indexing diffraction patterns, superspace, ab initio methods, ...
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This chapter discusses the X-ray and neutron diffraction methods used to study the atomic structures of aperiodic crystals, addressing indexing diffraction patterns, superspace, ab initio methods, the structure factor of incommensurate structures; and diffuse scattering. The structure solution methods based on the dual space refinements are described, as they are very often applied for the resolution of aperiodic crystal structures. Modulation functions which are used for the refinement of modulated structures and composite structures are presented and illustrated with examples of structure models covering a large spectrum of structures from organic to inorganic compounds, including metals, alloys, and minerals. For a better understanding of the concept of quasicrystalline structures, one-dimensional structure examples are presented first. Further examples of quasicrystals, including decagonal quasicrystals and icosahedral quasicrystals, are analysed in terms of increasing shells of a selected number of polyhedra. The notion of the approximant is compared with classical forms of structures.Less
This chapter discusses the X-ray and neutron diffraction methods used to study the atomic structures of aperiodic crystals, addressing indexing diffraction patterns, superspace, ab initio methods, the structure factor of incommensurate structures; and diffuse scattering. The structure solution methods based on the dual space refinements are described, as they are very often applied for the resolution of aperiodic crystal structures. Modulation functions which are used for the refinement of modulated structures and composite structures are presented and illustrated with examples of structure models covering a large spectrum of structures from organic to inorganic compounds, including metals, alloys, and minerals. For a better understanding of the concept of quasicrystalline structures, one-dimensional structure examples are presented first. Further examples of quasicrystals, including decagonal quasicrystals and icosahedral quasicrystals, are analysed in terms of increasing shells of a selected number of polyhedra. The notion of the approximant is compared with classical forms of structures.
Anthony Stone
- Published in print:
- 2013
- Published Online:
- May 2013
- ISBN:
- 9780199672394
- eISBN:
- 9780191751417
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199672394.001.0001
- Subject:
- Physics, Atomic, Laser, and Optical Physics
The theory of intermolecular forces has advanced very greatly in the last few decades. Simple empirical models are no longer adequate to account for the detailed and accurate experimental ...
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The theory of intermolecular forces has advanced very greatly in the last few decades. Simple empirical models are no longer adequate to account for the detailed and accurate experimental measurements that are now available, or to predict properties such as the structures of molecular crystals reliably. At the same time computational methods for calculating intermolecular forces have improved enormously, so that it is possible to construct much more accurate intermolecular potential energy functions for much larger systems than was possible twenty years ago. The Theory of Intermolecular Forces describes these advances. It sets out the mathematical techniques that are needed to describe molecular properties and the ways that they contribute to the interactions between molecules. There is a detailed account of the use of multipole moments to describe electrostatic and related interactions, and both Cartesian and spherical tensor methods are described. Perturbation theories of intermolecular interactions, in particular the widely-used SAPT and SAPT-DFT methods, are discussed in detail. The many analytic models of intermolecular potentials are described and discussed, and the methods used to predict experimental properties from them are described.Less
The theory of intermolecular forces has advanced very greatly in the last few decades. Simple empirical models are no longer adequate to account for the detailed and accurate experimental measurements that are now available, or to predict properties such as the structures of molecular crystals reliably. At the same time computational methods for calculating intermolecular forces have improved enormously, so that it is possible to construct much more accurate intermolecular potential energy functions for much larger systems than was possible twenty years ago. The Theory of Intermolecular Forces describes these advances. It sets out the mathematical techniques that are needed to describe molecular properties and the ways that they contribute to the interactions between molecules. There is a detailed account of the use of multipole moments to describe electrostatic and related interactions, and both Cartesian and spherical tensor methods are described. Perturbation theories of intermolecular interactions, in particular the widely-used SAPT and SAPT-DFT methods, are discussed in detail. The many analytic models of intermolecular potentials are described and discussed, and the methods used to predict experimental properties from them are described.
Eric Smith, Harold J. Morowitz, and Shelley D. Copley
- Published in print:
- 2008
- Published Online:
- August 2013
- ISBN:
- 9780262182683
- eISBN:
- 9780262282093
- Item type:
- chapter
- Publisher:
- The MIT Press
- DOI:
- 10.7551/mitpress/9780262182683.003.0020
- Subject:
- Biology, Microbiology
This chapter focuses on the numerical approaches for protocell simulation. It discusses the ab initio methods, semiempirical methods, molecular mechanics or molecular dynamics (MM or MD), quantum ...
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This chapter focuses on the numerical approaches for protocell simulation. It discusses the ab initio methods, semiempirical methods, molecular mechanics or molecular dynamics (MM or MD), quantum mechanics and molecular mechanics, coarse-grained molecular dynamics, the lattice Boltzmann (LB) method, and the Ginzburg-Landau (GL) models, and the multiscale methods.Less
This chapter focuses on the numerical approaches for protocell simulation. It discusses the ab initio methods, semiempirical methods, molecular mechanics or molecular dynamics (MM or MD), quantum mechanics and molecular mechanics, coarse-grained molecular dynamics, the lattice Boltzmann (LB) method, and the Ginzburg-Landau (GL) models, and the multiscale methods.
