Point defect: also magnetic

It is not possible to give here a complete review of DMol applications, so only a non-systematic selection of applications is mentioned here. Applications to chemical reactions have been studied by Seminario, Grodzicki and Politzer [10]. Buckminster-fullerenes have been studied by various groups [11] including also nonlinear optical properties [8] and the geometrical structure of Cs4 [13]. Cluster model studies of surfaces with adsorbates are reported in [14-17]. Cluster models for point defects in solids, in particular spin density studies of interstitial muon can be found in [18,19]. Spin density studies of molecular magnetic materials are in ref [20]. Polymers have been studied by Ye et al [21]. 

Complete structural characterization of a material involves not only the elemental composition for major components and a study of the crystal structure, but also the impurity content (impurities in solid solution and/or additional phases) and stoichiometry. Noncrystalline materials can display unique behavior, and noncrystalline second phases can alter properties. Both the long-range order and crystal imperfection or defects must be defined. For example, the structural details which influence properties of oxides include the impurity and dopant content, nonstoichiometry, and the oxidation states of cations and anions. These variables also influence the point-defect structure, which in turn influences chemical reactivity, and electrical, magnetic, catalytic, and optical properties. 

It is worthwhile to examine the Hamiltonian in some detail because it enables one to discuss both intramolecular and intermolecular perturbations from the same point of view. To do so, we start from a zero-order Hamiltonian that contains just the spherical part of the field due to the core (which need not be Coulombic as it includes also the quantum defect [42]) and add two perturbations. U due to external effects and V due to the structure of the core. Here, U contains both the effect of external fields (electrical and, if any, magnetic [1]) and the role of other charges that may be nearby [8, 11, 12, 17]. The technical point is that both the effect of other charges and the effect of the core not being a point charge are accounted for by writing the Coulomb interaction between two charges, at points ri and r2, respectively, as... 

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