In this review, we present some relationships between first-principles electronic structure calculations and experiments. Actually, many theoretical and experimental researchers feel an invisible barrier to each other. The purpose of this review is to enhance the understanding each other. We take some examples of the electronic structure calculations and related experiments and discuss this problem.
Not only limited to the first-principles calculation, but also for all simulations using computers, it must be pointed out that the output results could be calculated even from the wrong input data or/and unphysical models. Therefore it is necessary to check the calculated results carefully. In this paper, the sampled k-point, cutoff energy, and pseudopotentials are briefly explained to understand the calculational conditions systematically. Then calculated examples are shown for some typical models.
Structure optimizations are fundamental techniques in first-principles calculations. From the structure optimization, we can determine a wide range of things, such as lattice constants of crystals, the spacing between a surface atom layer and a subsurface layer, and the adsorption sites of adsorbates. This paper discusses the structure optimization methods and the relating methods. First, the paper discusses the requirement of highly accurate total energies and its effect on the treatment of the calculated total energies. Second, two common algorithms utilizing atomic forces for the structure optimization are introduced. Third, the error in the optimization is discussed. It can be classified into two groups. The first one comes from how the electronic correlation is treated. The second one comes from the numerical convergence of the calculation. Last, as advanced topics, methods for (free) energy barrier are briefly introduced.
Recent trends in quantum chemical calculations for surface-molecule interacting systems are explained mainly by introducing the theoretical studies of our group. This paper first compares the features of quantum chemical calculations based on the molecular orbital (MO) method and the density functional theory (DFT). Next, we illustrate both fundamental and advanced subjects on the modelling of the surface-molecule interacting systems: namely, a cluster model and a periodic model. A novel analytical technique of the quantum chemical calculations, that is, energy density analysis (EDA) is introduced by using several examples.
In order to help those who want to learn first-principles calculations, specification requirements for a computing machine will be shown and a few of first-principles calculation packages will be introduced.
X-ray diffraction studies have been carried out on stratum corneum (SC) intensively. The results provide an evidence for the relationship between the microstructure and the characteristic of SC. In this paper, based on the microscopic evidence, we will show first the characteristic of the barrier function of SC, second the relationship between the barrier function and the structure of SC, and third the reconstitution of the damaged SC when it is immersed in a dilute aqueous suspension of mixture of ceramide, cholesterol and fatty acid that are dominant components in the intercellular lipid matrix.
Recently, the miniaturization limits of fabrications have approached the order of molecular size. In order to measure the electric characteristics of a single molecule, it is necessary to fabricate not only the molecular-sized nanogap electrodes but also the stable chemical bonds established from a single molecule to two facing electrodes. In this paper, the author demonstrated a procedure for fabricating molecular-sized nanogap electrodes and a steadiness of the bridge-structure depending on molecular structure of bridge-molecules.