Properties of Atoms, Ions, Molecules, and Solids

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. 

Porous solids are of scientific and technological importance because of their ability to interact with atoms, ions, molecules, and supramolecules [1]. The presence of voids of controllable dimensions at the atomic, molecular, and nanometer scales in porous solids endows them with unique interfadal properties [2], As a result, they are widely used as ion-exchangers, adsorbents, catalysts, and catalyst supports. Structurally, they are classified into microporous, mesoporous, and macroporous solids, with pore sizes of less than 2 nm, from 2 to 50 nm, and larger than 50 nm, respectively. Compositionally, they could be inorganic, polymeric, and composite [1-8]. 

This chapter provides a cursory introduction to the atom s structnre and the properties that result when two or more atoms/ions bind to each other. This includes a discussion on the electronic structure (the distribution of the electrons within an atom, ion, molecule, or solid) in ground or excited states. These are considered important because, as introduced in Section 1.1, the properties of matter are dictated by the type of elements present and how they bond to each other (this can include the long-range lattice structure). Electronic excitations are included because, as covered within Sections 3.2 and 3.3, sputtering can impart a substantial amount of energy into the bound system, which in turn can influence secondary ion yields. 

The macroscopic properties of a material are related intimately to the interactions between its constituent particles, be they atoms, ions, molecules, or colloids suspended in a solvent. Such relationships are fairly well understood for cases where the particles are present in low concentration and interparticle interactions occur primarily in isolated clusters (pairs, triplets, etc.). For example, the pressure of a low-density vapor can be accurately described by the virial expansion,1 whereas its transport coefficients can be estimated from kinetic theory.2,3 On the other hand, using microscopic information to predict the properties, and in particular the dynamics, of condensed phases such as liquids and solids remains a far more challenging task. In these states... 

It is apparent that progress in our understanding of the properties of neutral heavy elements and their ions, including very highly ionized ones, as well as their role as constituents of molecules and solids, will depend on the development of theoretical methods and computational techniques, which are based on relativistic quantum mechanics. Fairly efficient methods of this kind have already been elaborated and many versions of relativistic codes for work with isolated atoms and ions are already available and in daily use by internationally known theoretical and experimental physicists and chemists [18, 54-57],... 

Detailed observations and assignments of the giant resonances in many free atoms then followed rapidly, guided by the earlier observations for the solid. It was soon established experimentally that the quasiatomic giant resonances occur for nearly all solids for which the corresponding atomic transition exists, and that they may persist both in molecules and in ions. A detailed discussion of the properties of giant resonances in atoms, molecules and solids may be found in the book Giant Resonances in Atoms, Molecules and Solids [191], which summarises much of the research in this area prior to 1986. 

A crystal lattice is formed by a repeated arrangement of atoms, ions, or molecules. Within one cubic centimetre of material one can expect to find up to 10 atoms and it is extremely unlikely that all of these will be arranged in perfect order. Some atoms will not be exactly in the right place with the result that the lattice will contain defects. The presence of defects within the crystal structure has profound consequences for certain bulk properties of the solid, such as the electrical resistance and the mechanical strength. 

Crystalline solids consist of atoms, ions, or molecules that are arrayed into a long-range, regularly ordered structure known as a crystalline lattice. A crystal consists of a pattern of objects that repeats itself periodically in three-dimensional space, so that it has the property of translational symmetry. A lattice is simply a three-dimensional array of lattice points, where the atoms, ions, or molecules are held together in the solid state by a balance of attractive and repulsive forces. Lattice points are geometrical constructs it is not a necessary condition for a physical entity, such as an atom or ion, to actually occupy the lattice point Indeed, many lattice points are simply empty space, around which a basis, or motif, of particles is centered. Two examples of two-dimensional lattices are shown in Figure 11.1. 

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