COMPUTATIONAL PHYSICS. Research: multi-tools to study physical and chemical properties of materials at different time and length scales.

Transcription

1 COMPUTATIONAL PHYSICS Aniket Bhattacharya 1 GS + 1UGS Archana Dubey - Abdelkader Kara 1 UGS Talat Rahman 7 GS + 1 REU PostDocs Patrick Schelling 2 GS + 1UGS + 3 REU Sergey Stolbov 1GS ~ 30 papers in the last 12 months Research: multi-tools to study physical and chemical properties of materials at different time and length scales. Development: new tools to extend the accuracy and speed of simulations to larger length and time scales

2 Organic Materials Pentacene/Cu(110) Adsorption energy: 1.49 ev Abdelkader KARA RESEARCH Pentacene on p(2x1)o /Cu(110) [0 0 1][1 1 0] Silicene Nano-Ribbons: Si/Ag(110) Diffusion barrier: 150 mev Charge transfer Sexithiophene on Ag(110) Side view Interface states : theory and Experiment Confinement 0.7 ML Diffusion barrier: 66 mev 0.8 ML (E-E F ) (ev) 1 ML Azimuthal angle (degrees) akara@mail.ucf.edu

3 On Lattice Recognition Start End Abdelkader KARA DEVELOPMENT Self-Learning Kinetic Monte Carlo In collaboration with Rahman s group Go over all atoms and determine all processes which are possible. Γ (i) = Γ (i) o exp(-δe (i ) /k B T) adjust the clock: 1/R Do process k, i.e. move one atom (randomly chosen) yes If novel Configuration occurs: no Calculate E Data base get two random numbers r 1, r 2 from [0,1[ Calculate R = ΣΓ (i) and find process k from the data base: Σ k Γ (i) > r 1 R > Σ k- 1 Γ (i) D 0 T PREFACTORS N N 1 D 0 / k B T h 2 nd 2 i i 1 j 1 S exp k B vib j U exp k B T Concerted Motion vib Off Lattice Recognition Gain in Speed and Precision Experiment SL-KMC simulation akara@mail.ucf.edu

4 Dr. Archana Dubey Aim: Understanding of proteins and enzymes at functional levels. Procedure: Hartree-Fock- Cluster procedure implemented by the Roothaan variational approach. The model system to simulate deoxy hemoglobin consists of a heme unit with imidazole of the proximal histidine attached to the Fe atom on the heme unit through one of the two N in the imidazole, namely the apex N ε in the figure. Peripheral carbons of the pyrroles in the heme unit are terminated by H atoms. Fe atom is rather internal in the central region of the heme unit, and the adjustments made in the peripheral regions of the heme are not expected to influence the electron distribution significantly in the neighborhood of the 57m Fe nucleus.

5 Multiscale simulation of mass and heat transport Patrick K. Schelling, University of Central Florida Multiscale simulation of laser ablation decompressor are needed to see this picture. Complex oxides and geophysics Atomistic models with excited electrons Electron-phonon scattering Combined phonon/electron transport Oxides for thermal barrier coatings Point-defect scattering, disorder Transport in MgSiO 3 up to p=120gpa NSF-DMR NSF-REU Nanoscale thermal transport Effect of discrete phonon spectra Size-dependence of interfacial resistance Interfacial thermal transport and phonon dynamics Scattering simulation/theory Transport in nanocrystalline materials Cross-sectional view of simulated Si nanowires Phonon scattering at Si grain boundary

6 First principles studies of stability and reactivity of electro-catalysts for low-temperature fuel cells Sergey Stolbov, Associate Professor, Physics Dept. UCF Stability: Search for new materials to replace unacceptably expensive Pt in electrodes of low-temperature fuel cells (FC) is an important and challenging problem for electro-catalysis. Promising electro-catalysts such as Ru nanoparticles with the Pt (Pt/Ru) and Se (Se/Ru) sub-monolayer coverage have a complex geometric structure that makes their stability an issue of concern. We apply the density functional theory (DFT) based computational approach to reveal key characteristics of stability of these materials. Island formation energy per/atom of Pt (right panel) and Se (left panel) as a function of the island size Pt/Ru M. Alcantara Ortigoza, S. Stolbov and T. S. Rahman, PRB, 78, Se/Ru S. Stolbov, in preparation We find that Pt atoms tend to join into large 2D islands by making Pt-Pt and Pt-Ru covalent bonds, while Se atoms charged by electron transfer form the surface repeal and hence prefer stay apart from each other on the substrate. Work in progress: In collaboration with M. Alcantara Ortigoza and T. S. Rahman we are studying electronic structure and energetics of layered Ru/Pt and Ru/Pt/Ru structures to explain character of growth of such structures observed in experimental works by R.J. Behm and co-workers (Vacuum 84, 13 (2010), Surf. Sci. 603, 2556 (2009)). With graduate student S. Zuluaga we begun studying geometric and electronic structures of Se-Ru nano-clusters..1.2

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