First principles calculations are used to investigate carbonated hydroxyapatite, a naturally occurring mineral and also the inorganic component of animal bone. Two types of carbonate substitution are studied:  A-type in which the carbonate ion substitutes for an OH and B-type where the substitution is for a phosphate. Both types have unbalanced charges and various forms of charge compensation are treated. The methods, which are based on density functional theory and first principles pseudopotentials, yield equilibrium atomic arrangements, changes in lattice parameters, and total energies for different types of substitution. When calculated energies of selected stable compounds are used, the formation energies of different carbonate substitutions with accompanying charge compensation defects can be compared. The results indicate that compact complexes are energetically favored, and a B-type material with charge compensation by a calcium vacancy together with a hydrogen atom which bonds to a neighboring phosphate is the most stable of all those considered.

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We have investigated various silica zeolites using density functional theory with periodic supercells, plane waves, and pseudopotentials. These zeolitic phases include silica sodalite, chabazite, mordenite, silica LTA, and silicalite. Atom-level geometries, elastic properties, and cohesive energies are presented. Although the zeolites exhibit a wide range of Si−O−Si angles and densities, the cohesive energies remain nearly constant. The elastic properties vary significantly from one phase to another, and in some cases, large elastic anisotropies are observed.

The electrical properties of SrTiO 3 are strongly dependent on the oxygen vacancy concentration. We have studied the atomic and electronic properties of a single oxygen vacancy using a local spin density approximation-planewave pseudopotential method. The total energies, relaxed geometries, valence charge and spin densities, and densities of electron states are calculated for different charge states of the vacancy. The doubly positively charged state is found to be the most stable. With some charge states, a spin-polarized defect state is observed. Furthermore, we have evaluated the formation energy of the vacancy in the O O → V O + 1 2 O 2 process.

All-silica zeolite frameworks doped with methylene and amine groups are studied using density functional theory-based electron structure calculations. Strain energies are calculated in a novel way, by comparing zeolite energies with appropriate polymer reference systems. The modified zeolites are found to be mechanically stable structures with surprisingly little strain. Distortions due to impurities result in broadened Si-O-Si angle distributions in the lattice surrounding defects. Our results suggest that zeolites can accommodate both methylene and amine groups at high concentrations with minimal strain. The amine-doped zeolites are strong Lewis bases suggesting novel applications in base catalysis.