Model reconstructions for the Si(337) orientation

Although unstable, the Si(337) orientation has been known to appear in diverse experimental situations such as the nanoscale faceting of Si(112), or in the case of miscutting a Si(113) surface. Various models for Si(337) have been proposed over time, which motivates a comprehensive study of the structure of this orientation. Such a study is undertaken in this article, where we report the results of a genetic algorithm optimization of the Si(337)-$(2\times 1)$ surface. The algorithm is coupled with a highly optimized empirical potential for silicon, which is used as an efficient way to build a set of possible Si(337) models; these structures are subsequently relaxed at the level of ab initio density functional methods. Using this procedure, we retrieve most of the (337) reconstructions proposed in previous works, as well as a number of novel ones.Comment: 5 figures (low res.); to appear in J. Appl. Phy

Electronic Structure and Optical Properties of Silicon Nanocrystals along their Aggregation Stages

The structural control of silicon nanocrystals is an important technological problem. Typically a distribution of nanocrystal sizes and shapes emerges under the uncontrolled aggregation of smaller clusters. The aim of this computational study is to investigate the evolution of the nanocrystal electronic states and their optical properties throughout their aggregation stages. To realistically tackle such systems, an atomistic electronic structure tool is required that can accommodate about tens of thousand nanocrystal and embedding lattice atoms with very irregular shapes. For this purpose, a computationally-efficient pseudopotential-based electronic structure tool is developed that can handle realistic nanostructures based on the expansion of the wavefunction of the aggregate in terms of bulk Bloch bands of the constituent semiconductors. With this tool, the evolution of the electronic states as well as the polarization-dependent absorption spectra correlated with the oscillator strengths over their aggregation stages are traced. The low-lying aggregate nanocrystal states develop binding and anti-binding counterparts of the isolated states. Such information may become instrumental with the maturity of the controlled aggregation of these nanocrystals.Comment: 5 pages, 7 figure

Finite Element Analysis of Finite Deformation Problems for Bio-Polymer Materials

[[abstract]]For shape maintenance and migration of living organisms, bio-polymer materials play important roles for the redistribution of internal forces in the biological structures. A substantial amount of observations have been made over the past decades to show how the structures composed of bio-polymers deform and identify what the characteristics of the network materials are. For example, it has been revealed both experimentally and computationally that as macroscopic loading goes, the bio-polymer materials of the network type experience alterations from entropy-directed shape changes to structural deformations, such as filament bending and stretching. In addition, the transition point happens as the levels of macroscopic stress reach around 1% of the bulk modulus of the materials (Lin et al.2014). Hence, here finite element formulations are developed to solve the large deformation problems for the bio-polymer materials in solutions by introducing fluid-solid interaction forces across the immersed boundaries of the materials. Weanticipate that this technique will open doors for understanding more physiological states of biological specimens under environmental loading.[[sponsorship]]HCMC University of Technology[[conferencetype]]國際[[conferencedate]]20160106~20160108[[booktype]]紙本[[iscallforpapers]]Y[[conferencelocation]]Ho Chi Minh City, Vietna

Finite Element Modeling of Mechanical Behavior Variation of Collagen Fibrils under Different Concentration of Saline Solutions

[[abstract]]For shape maintenance and migration of living organisms, bio-polymer materials play important roles for the redistribution of internal forces in the biological structures. A substantial amount of observations have been made over the past decades to show how the structures composed of bio-polymers deform and identify what the characteristics of the network materials are. For example, it has been revealed both experimentally and computationally that as macroscopic loading goes, the bio-polymer materials of the network type experience alterations from entropy-directed shape changes to structural deformations, such as filament bending and stretching. In addition, the transition point happens as the levels of macroscopic stress reach around 1% of the bulk modulus of the materials. Hence, here finite element formulations are developed to solve the large deformation problems for the bio-polymer materials in solutions by introducing fluid-solid interaction forces across the immersed boundaries of the materials. We anticipate that this technique will open doors for understanding more physiological states of biological specimens under environmental loading.[[sponsorship]]Department of Mechanical Engineering, National Taiwan University of Science and Technology[[conferencetype]]國內[[conferencedate]]20151120-20151121[[booktype]]紙本[[iscallforpapers]]Y[[conferencelocation]]Taipei, Taiwa

Quantum gates on hybrid qudits

We introduce quantum hybrid gates that act on qudits of different dimensions. In particular, we develop two representative two-qudit hybrid gates (SUM and SWAP) and many-qudit hybrid Toffoli and Fredkin gates. We apply the hybrid SUM gate to generating entanglement, and find that operator entanglement of the SUM gate is equal to the entanglement generated by it for certain initial states. We also show that the hybrid SUM gate acts as an automorphism on the Pauli group for two qudits of different dimension under certain conditions. Finally, we describe a physical realization of these hybrid gates for spin systems.Comment: 8 pages and 1 figur

Structure of Si(114) determined by global optimization methods

In this article we report the results of global structural optimization of the Si(114) surface, which is a stable high-index orientation of silicon. We use two independent procedures recently developed for the determination of surface reconstructions, the parallel-tempering Monte Carlo method and the genetic algorithm. These procedures, coupled with the use of a highly-optimized interatomic potential for silicon, lead to finding a set of possible models for Si(114), whose energies are recalculated with ab-initio density functional methods. The most stable structure obtained here without experimental input coincides with the structure determined from scanning tunneling microscopy experiments and density functional calculations by Erwin, Baski and Whitman [Phys. Rev. Lett. 77, 687 (1996)].Comment: 19 pages, 5 figure