CVM-based first-principles calculations for Fe-based alloys

Phase Field Method ◽

Variation Method ◽

Probability Method ◽

First Principles Calculations ◽

Wide Range ◽

Cluster Variation ◽

Alloy Systems

ABSTRACTCluster Variation Method (CVM) has been recognized as one of the most reliable theoretical tools to incorporate wide range of atomic correlations into a free energy formula. By combining CVM with electronic structure total energy calculations, one can perform first-principles calculations of alloy phase equilibria. The author attempted such CVM-based first-principles calculations for various alloy systems including noble metal alloys, transition-noble alloys, III-V semiconductor alloys and Fe-based alloy systems. Furthermore, CVM can be extended to two kinds of kinetics calculations. One is Path Probability Method (PPM) which is the natural extension of the CVM to time domain and is quite powerful to investigate atomistic kinetic phenomena. The other one is Phase Field Method (PFM) with the CVM free energy as a homogeneous free energy density term in the PFM. The author’s group applied the latter procedure to study time evolution process of ordered domains associated with disorder-L10 transition in Fe-Pd and Fe-Pt systems. CVM has, therefore, a potential applicability for the systematic studies covering atomistic to microstructural scales. It has been, however, pointed out that the conventional CVM is not able to include local lattice relaxation effects and that the resulting order-disorder transition temperatures are overestimated. In order to circumvent such inconveniences, Continuous Displacement Cluster Variation Method (CDCVM) has been developed. Since first-principles CDCVM calculations are still beyond the scope at the present stage, preliminary results on the two dimensional square lattice and an fcc lattice with primitive Lennard-Jones type potentials are demonstrated in the last section.

Phase Field Calculations with CVM Free Energy within Square Approximation

10.4028/www.scientific.net/msf.561-565.1935 ◽

2007 ◽

Vol 561-565 ◽

pp. 1935-1940

Author(s):

Tetsuo Mohri ◽

Nao Fujihashi ◽

Ying Chen

Keyword(s):

Free Energy ◽

Phase Field ◽

Stoichiometric Composition ◽

Sharp Decrease ◽

Field Method ◽

Phase Field Method ◽

Square Lattice ◽

Variation Method ◽

Phase Field Method is combined with the Cluster Variation Method within the square approximation, and the multiscale ordering behavior from atomistic to microstructural evolution process of ordered domains in the two dimensional square lattice is investigated. The transition temperature is determined at 1:1 stoichiometric composition and it is confirmed that the transition is of the second order. The growth process of the ordered domains is visualized and it is revealed that the sharp decrease of the free energy takes place during the process.

Towards the First-Principles Investigation of Ordering Dynamics

10.4028/www.scientific.net/msf.475-479.3075 ◽

2005 ◽

Vol 475-479 ◽

pp. 3075-3080 ◽

Cited By ~ 5

Author(s):

Tetsuo Mohri ◽

Munekazu Ohno ◽

Ying Chen

Keyword(s):

First Principles ◽

Coarse Graining ◽

Field Method ◽

Energy Functional ◽

First Principles Calculation ◽

Phase Field Method ◽

Variation Method ◽

Gradient Energy ◽

Phase Field Method (PFM) is hybridized with Cluster Variation Method (CVM) to investigate the ordering dynamics of L10-disorder transition at atomistic and microstructural scales simultaneously. For this, coarse graining operation is attempted on the inhomogeneous free energy functional of CVM. The resultant gradient energy coefficient is found out to be dependent on temperature and order parameters, which is in marked contrast to a conventional PFM formalism. Electronic structure total energy calculations for Fe-Pd system are incorporated to the hybridized scheme and the first principles calculation of microstructural evolution process is attempted.

From Phase Equilibria to Transformation Dynamics

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.263.21 ◽

2007 ◽

Vol 263 ◽

pp. 21-30 ◽

Cited By ~ 1

Author(s):

Tetsuo Mohri ◽

Munekazu Ohno ◽

Ying Chen

Keyword(s):

Phase Transformation ◽

Phase Equilibria ◽

First Principles ◽

Materials Science ◽

Present Report ◽

First Principles Calculation ◽

Phase Field Method ◽

Variation Method ◽

First Principles Calculations

First principles calculations have been applied in various fields in Materials Science. The authors have been attempting to reproduce a binary phase diagram by combining FLAPW electronic structure total energy calculations with Cluster Variation Method of statistical mechanics. Such a first principles calculation for static equilibrium has been quite successful for a series of Febased alloy systems. Recently, main attention is directed towards the extension of the first principles calculation to phase transformation dynamics by incorporating Phase Field Method. A series of preliminary calculations on disorder-L10 ordering in Fe-Pd and –Pt are satisfactory and the evolution process of Anti-Phase Boundaries was reproduced. In the present report, first-principles calculations of phase equilibria and phase transformation are briefly reviewed. Particular focuses are placed on coarse graining operation which authors developed and and time scaling as a remaining problem.

Theoretical Study of Glass Transition Based on Cluster Variation Method

10.4028/www.scientific.net/msf.539-543.2425 ◽

2007 ◽

Vol 539-543 ◽

pp. 2425-2430 ◽

Cited By ~ 1

Author(s):

Tetsuo Mohri ◽

Yoshitaka Kobayashi

Keyword(s):

Free Energy ◽

Glass Transition ◽

Order Parameter ◽

Variation Method ◽

Bravais Lattice ◽

Probability Method ◽

Temperature Dependent Viscosity ◽

Viscosity Term ◽

Modeling of Glass transition is attempted based on the Cluster Variation Method. Free energy functional of an L10 ordered phase is employed to describe the first order nature of the transition. Free energy contour surface calculated as a function of temperature and an order parameter which simulates an amount of defects provides a generalized stability diagram in which the ideal glass transition temperature is identified as a critical point. Transition kinetics is investigated by Path Probability Method which is the kinetics version of the CVM to time domain. Continuous cooling behavior is calculated by explicitly incorporating the temperature dependent viscosity term based on VFT (Vogel-Fulcher-Tamman) formula. The glass transition is realized as the freezing of the order parameter due to the enhanced viscosity. The extension of the present theoretical scheme to non-Bravais lattice is attempted by Continuous Cluster Variation Method.

Multi-Scale Phase Field Simulation of Disorder-Order Transition, Combined with Cluster Variation and Path Probability Methods

10.4028/www.scientific.net/msf.631-632.401 ◽

2009 ◽

Vol 631-632 ◽

pp. 401-406

Author(s):

Munekazu Ohno ◽

Ying Chen ◽

Tetsuo Mohri

Keyword(s):

Phase Field ◽

Field Method ◽

Phase Field Method ◽

Variation Method ◽

Probability Method ◽

Multi Scale ◽

Probability Methods ◽

Cluster Variation ◽

Path Probability Method

Multi-scale simulation of ordering process from electronic, atomistic scales to microstructural scale was carried out by hybridizing Phase Field Method (PFM) and Cluster Variation Method (CVM). The hybrid model was applied to disorder-L10 ordering process in Fe-Pd system. Furthermore, computation of relaxation constants in the PFM was attempted based on Path Probability Method (PPM) which is the time evolution version of the CVM, within a linearized analysis of order-order relaxation process.

First-principle Thoery of Phase Stability, Phase Equilibria and Phase Transition of Ordered Compounds

MRS Proceedings ◽

10.1557/proc-980-0980-ii02-01 ◽

2006 ◽

Vol 980 ◽

Author(s):

Tetsuo Mohri

Keyword(s):

Electronic Structure ◽

First Principles ◽

Future Prospect ◽

First Principles Calculation ◽

Variation Method ◽

Cluster Variation ◽

The Stability ◽

Noble Metal Alloys ◽

Alloy Systems

AbstractFirst-principles theory of alloys is based on electronic structure calculation at the ground state and statistical mechanics calculation at finite temperatures. The former clarifies the stability of an ordered compound against competing phases and the latter is employed mainly to derive a phase diagram. The author performed a series of first-principles investigations on binary alloy systems including noble metal alloys, semiconductor alloys and Fe-based alloy systems by combining FLAPW electronic structure total energy calculations with Cluster Variation Method. Recently, the theoretical framework is extended even to calculate microstructural evolution process. By exemplifying Fe-based alloy systems, the progress of the first-principles calculation is reviewed and future prospect is discussed.

Multicritical phase diagrams of the ferromagnetic spin- Blume–Emery–Griffiths model with repulsive biquadratic coupling including metastable phases: The cluster variation method and the path probability method with the point distribution

Journal of Magnetism and Magnetic Materials ◽

10.1016/j.jmmm.2007.05.005 ◽

2008 ◽

Vol 320 (1-2) ◽

pp. 8-24 ◽

Cited By ~ 15

Author(s):

Mustafa Keskin ◽

Osman Canko

Keyword(s):

Phase Diagrams ◽

Metastable Phases ◽

Variation Method ◽

Probability Method ◽

Point Distribution ◽

Cluster Variation ◽

Path Probability Method

Theoretical Investigation of Coarsening Process of L10-Ordered Domain Based on Phase Field Method and Cluster Variation Method

MATERIALS TRANSACTIONS ◽

10.2320/matertrans.43.2189 ◽

2002 ◽

Vol 43 (9) ◽

pp. 2189-2192 ◽

Cited By ~ 6

Author(s):

Munekazu Ohno ◽

Tetsuo Mohri

Keyword(s):

Theoretical Investigation ◽

Phase Field ◽

Field Method ◽

Phase Field Method ◽

Variation Method ◽

A First Principles Examination of Phase Stability in Fcc-Based Ni-V Substitutional Alloys

MRS Proceedings ◽

10.1557/proc-186-83 ◽

1990 ◽

Vol 186 ◽

Author(s):

J. Mikalopas ◽

P.E.A. Turchi ◽

M. Sluiter ◽

P.A. Sterne

Keyword(s):

Phase Stability ◽

Ground State ◽

First Principles ◽

Variation Method ◽

Many Body ◽

Cluster Variation ◽

Many Body Interactions ◽

Ground State Energies ◽

Substitutional Alloys

AbstractThe phase stability of fcc-based Ni-V substitutional alloys is investigated using linear muffin-tin orbitals total energy (LMTO) calculations. The method of Connolly and Williams (CWM) is used to extract many body interactions from the ground state energies of selected ordered configurations. These interactions are used in conjunction with the cluster variation method (CVM) to calculate the alloy phase diagram. The dependence of the interactions on the choice of configurations used to calculate them is examined.

Theoretical Investigation of Alloy Phase Equilibria by Continuous Displacement Cluster Variation Method

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.172-174.1119 ◽

2011 ◽

Vol 172-174 ◽

pp. 1119-1127

Author(s):

Tetsuo Mohri

Keyword(s):

Phase Equilibria ◽

Lattice Point ◽

Lattice Points ◽

Variation Method ◽

Bravais Lattice ◽

Diffuse Intensity ◽

Wide Range ◽

Cluster Variation ◽

Continuous Displacement

Continuous Displacement Cluster Variation Method is employed to study binary phase equilibria on the two dimensional square lattice with Lennard-Jones type pair potentials. It is confirmed that the transition temperature decreases significantly as compared with the one obtained by conventional Cluster Variation Method. This is ascribed to the distribution of atomic pairs in a wide range of atomic distance, which enables the system to attain the lower free energy. The spatial distribution of atomic species around a Bravais lattice point is visualized. Although the average position of an atom is centred at the Bravais lattice point, the maximum pair probability is not necessarily attained for the pairs located at the neighboring Bravais lattice points. In addition to the real space information, k-space information are calculated in the present study. Among them, the diffuse intensity spectra due to short range ordering and atomic displacement are discussed.