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We report on the adsorption and manipulation of K atoms on a hydroxylated TiO2(110)-1×1 surface using low-temperature noncontact atomic force microscopy. At low coverage, first-principles GGA + U calculations reveal favorable adsorption sites that are consistent with the experimentally observed adsorption positions on the upper-threefold hollow site, in which the K atom is bound to two bridging-oxygen (Obr) and one in-plane oxygen atoms, forming an ionic bond with three oxygen by transferring almost one of the K 4s electrons to the substrate. K atoms can be manipulated preferentially along the [001] direction over the Obr row by the tip through attractive force. Density functional theory calculations have provided diffusion paths for the adsorbed K atoms, which indicate a channel that provides ease of diffusion for a single K atom along the Obr rows associated with an energy barrier of 0.21 eV.

First-principles calculations are performed to investigate atomic and electronic structures of Na+ and K+ ions substituting for Ca2+ in hydroxyapatite (HAp). Formation energies of the substitutional defects are obtained from total energies of defective HAp supercells and chemical potentials determined by assuming chemical equilibrium between HAp and HAp-saturated aqueous solution containing Na+ or K+. It is found that substitutional Na+ with a charge-compensating interstitial proton is more stably formed, as compared to substitutional K+. This may be related to the fact that Na+ is generally more abundantly involved in bones and tooth enamels than K+.

Atomic structures and ionic substitutions in sodium titanate (Na2−xHxTi3O7), having Ti3O7 sheetlike layers with Na+ and H+ in between, were investigated by first-principles calculations. The formation energies via ion exchange of Na+ and H+ were analyzed by using the supercell total energies and ionic chemical potentials determined with the aid of experimental thermodynamic data. It was found that ionic substitutions of Na+ by H+ take place even in alkaline solution conditions as found in previous experiments. In addition, the bonding strength between the Ti3O7 layers tends to decrease with more Na+ substitutions by H+, which is related to pH effects on exfoliation events of Ti3O7 sheetlike layers from layered titanate prior to the nanotube formation.

Co-L2, 3 x-ray-absorption near-edge structures (XANES) and electron-energy-loss near-edge structures (ELNES) are calculated from first principles, taking into account the configuration interactions among molecular orbitals for model clusters obtained using fully-relativistic one-electron calculations. The spectra for LaCoO3 at low temperature and for LiCoO2, both of which have low-spin Co3+ ions in similar local environments, are well reproduced. To elucidate the cause of the spectral shape, the effects of the crystal structure and coordination distance are investigated using idealized crystal structures of layered rock salt, perovskite, rock salt, and spinel. The calculated spectra for these crystals with the same coordination distance are found to show clear differences despite identical 3d electronic configurations and local environments of the first ligand shell. The crystal structure dependence can be explained by the difference in the Madelung potential acting on the 3d orbitals. The results of the calculations for various coordination distances indicate that not only the crystal field splitting parameter, namely, 10Dq, but also the coordination distance is a key factor in determining the spectral shape. This is attributed to the change in the spatial distribution of the 3d orbitals.

The lattice dynamics of three polymorphs of Si3N4, , , and phases, has been calculated by the real space force constant method combined with first-principles calculations. The thermodynamical properties of the three phases are evaluated from the vibrational density of states. The effect of thermal volume expansion is included by quasiharmonic approximation. The volume expansivity, bulk modulus, specific heat, and Helmholtz free energy of the three phases are computed as a function of temperature. All three phases are found to be dynamically stable. -Si3N4 shows lower Helmholtz free energy than -Si3N4 in the temperature range from 0 to 2000 K. In other words, -Si3N4 is not a low-temperature phase but a metastable phase under the ordinary pressure. The presence of planer N-Si3 units and their strong Si-N bonds in two hexagonal polymorphs, - and -Si3N4, is the origin of the high-frequency phonon band at above 25 THz, which is absent in -Si3N4. It plays key roles for anisotropic local vibration of N atoms. The different temperature dependence of specific heat between, and phases can also be ascribed to the structure. The transition pressure from to phase is computed as a function of temperature. It is found to increase with the rise of temperature.

First principles calculations are carried out to analyze adsorption of CO and H2 molecules on a Pt (111) surface and the effect of surface strain on the adsorption energy. A CO molecule is more adsorptive on the Pt (111) surface than a H2 molecule under an ordinary condition. Surface expansion enhances CO poisoning on a Pt (111) surface. On the contrary, a compressive strain reduces adsorptive strength of a CO molecule. Similar tendency is also found in adsorption of a H2 molecule on the bridge, fcc-hollow, and hcp-hollow sites. However, H2 adsorption on the top site is less affected by the strain. As a consequence, the difference of adsorption energies between CO and H2 molecules becomes smaller when compressive strain is introduced into the Pt (111) surface. Based on thermodynamics, surface coverage ratio is quantitatively evaluated with taking into account the effect of surface strain and partial pressure of gas phase. It is revealed that compressive strain improves probability of H2 adsorption on Pt surface.