Accurate estimation of a phase diagram from a single STM image.

We propose a new approach to constructing a phase diagram using the effective Hamiltonian derived only from a single real-space image produced by scanning tunneling microscopy (STM). Currently, there have been two main methods to construct phase diagrams in material science: ab initio calculations and CALPHAD with thermodynamic information obtained by experiments and/or theoretical calculations. Although the two methods have successfully revealed a number of unsettled phase diagrams, their results sometimes contradicted when it is difficult to construct an appropriate Hamiltonian that captures the characteristics of materials, e.

Direct evaluation of free energy for large system through structure integration approach.

We propose a new approach, 'structure integration', enabling direct evaluation of configurational free energy for large systems. The present approach is based on the statistical information of lattice. Through first-principles-based simulation, we find that the present method evaluates configurational free energy accurately in disorder states above critical temperature.

Surface design of alloy protection against CO-poisoning from first principles.

Pt-based alloy catalysts are of significant importance in fuel cells due to enhanced electrode reactivity and selectivity. Designing alloy surfaces suitable for catalyst via first-principles predictions has long played a central role in identifying promising candidates. We propose surface design for polymer electrolyte fuel cell (PEFC) based on the use of thermodynamically stable alloy surfaces.

Segregation of Pt(28)Rh(27) bimetallic nanoparticles: a first-principles study.

Based on a first-principles calculation combined with the cluster expansion technique and Monte Carlo statistical simulation, the segregation behavior of a Pt(28)Rh(27) cuboctahedral nanoparticle is examined. From the effective cluster interaction of the nanoparticle, we see a similar weak ordering tendency inside the nanoparticle to that for Pt-Rh bulk alloy. Below the bulk melting temperature of around 1700 K, we find strong Pt segregation to the surface of the nanoparticle.

Cluster expansion approach for transmutative lattice systems.

We propose a cluster expansion (CE) technique that can express any function of atomic arrangement on any given lattice with the same number of lattice points in a single formalism. In the proposed CE, two types of spin variable, σ and τ, on the base lattice and virtual lattice, respectively, are introduced. The former spin variable specifies the occupation of the constituent elements for each lattice point.

Prediction of superhard cubic boron-carbon nitride through first principles.

Superhard cubic boron-carbon nitride (c-BNC) in terms of bulk modulus along a composition range of (BN)((1-x))(C(2))(x) (0≤x≤1) is systematically explored by Monte Carlo simulations and cluster expansion techniques based on first-principles calculation. Bulk moduli for the c-BNC ordered structures are reasonably expanded up to quadruplet clusters, indicating that dependence of the bulk modulus on atomic arrangements is not simply attributed to pairwise interactions. A negative correlation can be seen between bulk modulus and formation energies, which is consistent with previous theoretical works.

First-principles study of phase equilibria in Cu-Pt-Rh disordered alloys.

Phase stability of Cu-Pt-Rh ternary disordered alloys is examined by a combination of cluster expansion techniques and Monte Carlo statistical simulation based on first-principles calculation. The sign of pseudo-binary ECIs indicates that neighboring Cu and Pt strongly prefer unlike-atom pairs, Pt and Rh weakly prefer unlike-atom pairs, and Cu and Rh atoms prefer like-atom pairs, indicating that the ternary alloy retains the ordering tendency of the constituent binary alloys. The formation energy of a random alloy at T = 1200 K exhibits a negative sign for a wide range of Pt-rich compositions, while at Pt-poor compositions of x≤0.

Pressure effects on the phase stability of cubic BNC ternary alloys.

Pressure effects on the phase stability of cubic BNC alloys were examined by Monte Carlo simulations and the cluster expansion technique based on first-principles calculations. At pressure P = 10 GPa, solution energy of neighboring B-N and C-C atoms into diamond and cubic BN are both higher than those at P = 0 GPa, indicating a decrease of solubility in c-BNC under applied pressure. Monte Carlo statistical simulation reveal that the applied pressure decreases solubility limits by almost half of those at P = 0 GPa.