Materials Modeling (Res Area)

Research Areas

Text Box: In-silico exploration of materials properties through high-end computation The need to design, understand and control material properties arise in the context of basic research, materials selection & design, reprocessing and a host of other contexts in the nuclear industry. The response of materials to radiation damage, phase stability of alloys, understanding chemical properties from an electronic structure point of view are some typical requirements. Many macroscopic properties of materials are influenced by processes which straddle huge dynamical range of length- and time-scales. The mechanisms through which macroscopic material properties emerge through these scales is ill understood and is frequently inaccessible to even state of the art experimental tools. Hence, there is a compelling need for virtual materials laboratories. World-wide, the development of powerful multiscale models is work still under progress and provides the broad context for the computational initiative undertaken at MSD. For this purpose, a modest Beowulf cluster consisting of 64 dual Xeon® CPU nodes with a peak performance of ~ 500 Gflops, was commissioned in April, 2008 at MSD. Powerful packages for electronic structure and molecular dynamics calculations like wien2k, vasp, siesta, pwscf, abinit, cpmd, dlpoly, lammps, moldy, gromacs have been installed. A brief account of the research done is given below. The field of nanomaterials research and development is a current area of great promise. Nanomaterials have novel electronic, optical, magnetic and mechanical properties. As an example, in one study, it was discovered that nanowires of Fe (as well as Fe1-xCox) form a half-metallic ferromagnet, and hence are potentially useful as a spintronic material. In a related study, electron transport in magnetic tunnel junctions was computed as a function of applied bias and temperature using Green’s function method. In another problem, ab-initio lattice dynamics calculations were used to obtain the phonon spectrum enabling interpretation of experimental data. In other studies, Density Functional calculations were employed to investigate phase stability of alloys and compounds. As an example, investigations on vanadium nitrides reveal the importance of vacancies for stabilizing the experimentally observed NaCl (δ-phase) in preference to the otherwise stable hexagonal WC and NiAs structures (figure 1). With present tools even complex organic and biological molecules are amenable to investigation. For example, the selectivity of Metal Imprinted Polymer (MIP) Vinyl benzyl Imino Di Acetate (VbIDA) (C26H26CoN2O8:Na) to cobaltous ions as compared to ferrous ions was investigated- a problem of relevance to waste management and decontamination programs. In the context of reprocessing, transport properties like the shear and bulk viscosities, thermal conductivity, etc, of hydrocarbons are being investigated using reverse non-equilibrium molecular dynamics. An ambitious program for the development of radiation resistant materials using ab initio molecular dynamics, Monte Carlo simulations and continuum theories leading to seamlessly integrated multiscale models is envisaged. In this context, the formation energy of vacancies and self ion interstitials, and binding between these, are studied. An in-house code for structural pattern recognition of defects is being developed. Figure 2 shows the time evolution of primary defects in the cascade produced by a primary knock-on atom with 3keV energy in bcc Fe at 100K. In metallurgy and materials selection study, the stability and response of oxide dispersion strengthened ferritic/martensitic steels under irradiation was investigated both experimentally and computationally. Figure 3 shows the model system of Y2O3 nanoclusters in bcc Iron currently investigated, in this context, through computation to interpret positron experiments. In summary, a broad based state of the art computational materials science activity with a rich repository of techniques is initiated which would be helpful in different areas of materials research and development undertaken by DAE. Positron density isosurface in blue color showing localization at interfacial vacancy cluster. Iron atoms at the interface are shown in yellow and remaining Fe atoms in super cell are removed for clarity. Green balls represent unrelaxed positions of 20 Fe vacancies distributed around Y2O3 cluster. Y and O atoms are shown in purple and red color respectively.

First-Principles Study of Ground-State Properties and Phase Stability of Vanadium Nitrides

Selectivity of Metal Imprinted Polymers (MIP)

Materials Modeling