Nobuko Ohba, Shuji Ogata

The International Conference on Computational & Experimental Engineering and Sciences, Vol.19, No.3, pp. 77-78, 2011, DOI:10.3970/icces.2011.019.077

Abstract We have been developing the concurrent-type, hybrid quantum-classical simulation scheme for various atomic processes at liquid-solid interfaces [1]. In this scheme, the density-functional theory (DFT) method is applied to the "quantum" region to calculate the electronic structure; while the semi-empirical inter-atomic potential, to the "classical" region. In this talk we review its recent developments both from methodology and application viewpoints.
In the hybrid simulation, the DFT method that is applied at each time-step to a cluster of typically a hundred atoms (i.e., the QM region) consumes most of the computation power. It is highly desirable… More >

K. Williams¹, T. Cagin^1,2

The International Conference on Computational & Experimental Engineering and Sciences, Vol.15, No.4, pp. 153-160, 2010, DOI:10.3970/icces.2010.015.153

Abstract Designing magnetic shape memory materials with practicable engineering applications requires a thorough understanding of their electronic, magnetic, and mechanical properties. Experimental and computational studies on such materials provide differing perspectives on the same problems, with theoretical approaches offering fundamental insight into complex experimental phenomena. Many recent computational approaches have focused on first-principles calculations, all of which have been successful in reproducing ground-state structures and properties such as lattice parameters, magnetic moments, electronic density of states, and phonon dispersion curves. With all of these successes, however, such methods fail to include the effects of finite temperatures,… More >

Che-Wun Hong^1,2, Chia-Yun Tsai¹

CMES-Computer Modeling in Engineering & Sciences, Vol.67, No.2, pp. 79-94, 2010, DOI:10.3970/cmes.2010.067.079

Abstract This paper describes the quantum mechanical simulation on the photonic properties of group-III nitride clusters, whose bulk types are common materials for light emitting diodes (LEDs). In order to emit different colors of light using the same semiconductor materials, it is possible to vary the band gap by controlling the quantum dot sizes or doping a third atom theoretically. Density functional theory (DFT) calculations are performed to analyze a set of binary (GaN)_n (3≤n≤32) and ternary In_xGa_1-xN (0≤x≤0.375) clusters to study their photonic characteristics. The ground state structures are optimized to calculate the binding energies using More >

Giacomo Landi¹, Surya R. Kalidindi²

CMC-Computers, Materials & Continua, Vol.16, No.3, pp. 273-294, 2010, DOI:10.3970/cmc.2010.016.273

Abstract In this paper, we present a computationally efficient multi-scale framework for predicting the local fields in the representative volume element of a multiphase material system subjected to thermo-mechanical loading conditions. This framework for localization relationships is a natural extension of our recent work on two-phase composites subjected to purely mechanical loading. In this novel approach, the localization relationships take on a simple structure expressed as a series sum, where each term in the series is a convolution product of local structure and the governing physics expressed in the form of influence coefficients. Another salient feature More >

O. U. Ojeda¹ and T. Çagınˇ ¹

CMC-Computers, Materials & Continua, Vol.16, No.2, pp. 127-174, 2010, DOI:10.3970/cmc.2010.016.127

Abstract The large discrepancy in length and time scales at which characteristic processes of energetic materials are of relevance pose a major challenge for current simulation techniques. We present a systematic study of crystalline energetic materials of different sensitivity and analyze their properties at different theoretical levels. Information like equilibrium structures, vibrational frequencies, conformational rearrangement and mechanical properties like stiffness and elastic properties can be calculated within the density functional theory (DFT) using different levels of approximations. Dynamical properties are obtained by computations using molecular dynamics at finite temperatures through the use of classical force fields. More >

Yusuke Kinoshita¹, Shin Hase¹, Nobutada Ohno¹

The International Conference on Computational & Experimental Engineering and Sciences, Vol.10, No.2, pp. 39-40, 2009, DOI:10.3970/icces.2009.010.039

Abstract Boron nitride nanotubes (BNNTs) have been found to be truly electrically insulating regardless of their diameters, chiralities and number of shells. On the other hand, a recent experimental work on multi-walled BNNTs has shown that electrical transport properties of the BNNTs change from insulating to semiconducting through a bending deformation. However, deformation-induced electrical effects in BNNTs have not been fully clarified yet. In the present work, HOMO-LUMO energy gaps of (5,0), (13,0), (21,0) single-walled BNNTs (SWBNNTs) and (5,0)@(13,0), (13,0)@(21,0) double-walled BNNTs (DWBNNTs) under flattening deformation have been investigated using first-principles density functional calculations. The LUMO More >

Mustafa Uludoğan¹, D. Paula Guarin¹, Zully E. Gomez¹, Tahir Cagin¹, William A. Goddard III²

CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 215-238, 2008, DOI:10.3970/cmes.2008.024.215

Abstract Aiming at a presentation of the utility of the state of art of first-principles methods (PBE flavor of Density Functional Theory, DFT) in the area of materials science and engineering, we present our studies of the equation of state and ferroelectric-paraelectricphase transition in several ferroelectric systems, including BaTiO₃, PbTiO₃, SrTiO₃, AgNbO₃, Pb_xBa_1-xTiO₃ and Sr_xBa_1-xTiO₃. We also report the Born effective charges, optical dielectric constant, and phonon dispersion relation properties from Density Functional Perturbation Theory. Computed results are compared with other theoretical results (which were mostly on BaTiO₃, PbTiO₃, cubic SrTiO₃ using various approaches, as well as experiments. The studies on More >