Pushing Computational Limits on the Earth Simulator: Nanotechnology Drug Delivery

Transcription

1 Pushing Computational Limits on the Earth Simulator: From Nanotechnology to Drug Delivery David Tománek Michigan State University Acknowledgements Savas Berber, University of Tsukuba, Japan Morinobu Endo, Shinshu University, Japan Mikio Iizuka, RIST Tokyo Noboru Jinbo, Toshiba Japan Young-Kyun Kwon, University of Massachusetts, Lowell Yoshiyuki Miyamoto, N.E.C. Tsukuba, Japan Hisashi Nakamura, RIST Tokyo Eiji Osawa, NanoCarbon Research Institute, Japan Angel Rubio, University of Pais Vasco, Spain Syogo Tejima, RIST Tokyo Mina Yoon, Oak Ridge National Laboratory Financial Support: NSF-NSEC NSF-NIRT JAMSTEC-ESC (Japan) RIST (Japan)

2 Outline Introduction - Pioneers of nanotechnology: Carbon fullerenes and nanotubes - Challenging problems: Microscopic processes in nanostructures - State of the art of computer simulations: Where are we now? Searching High-Dimensional Phase Spaces - Fusion of fullerenes in peapods - Fusion of nanotubes Molecular Dynamics Simulations in Engineering - High thermal conductivity of nanotubes - Defect tolerance of nanotubes at high temperatures Molecular Dynamics Simulations in Medicine - Designer targeted drug delivery systems Excited State Molecular Dynamics Simulations - Light-induced self-healing of defective nanotubes - Light-induced deoxidation of nanotubes Summary and Conclusions Review: David Tománek, Carbon-based nanotechnology on a supercomputer, Topical Review in J. Phys.: Condens. Matter 17, R413-R459 (2005). Pioneers of nanotechnology: Carbon fullerenes and nanotubes The C 60 buckyball and other fullerenes: - successful synthesis - potential applications: lubrication superconductivity H. W. Kroto and J. R. Heath and S. C. O'Brien and R. F. Curl and R. E. Smalley, Nature 318 (1985) Nanotubes: - successful synthesis - potential applications: composites Li-ion batteries medication delivery EMI shielding flat-panel displays super-capacitors fuel cells hydrogen storage Nanotubes in the core of carbon fibers: A. Oberlin, M. Endo, and T. Koyama, J. Crystal Growth 32 (1976)

3 Carbon nanotubes 1-20 nm diameter Atomically perfect Chemically inert 100 times stronger than steel Extremely high melting temperature Ideal (ballistic) conductors of electrons, or insulators Ideal heat conductors Non-toxic Nanotubes grow by decomposing carbon compounds to make bright flat-panel displays field-effect transistors for the next generation of computer chips Nanotube Field Effect Transistor or deliver drugs Nanotube

4 Challenging problems: Microscopic processes in nanostructures excited state etransport hν eeground state Can we help designing nanostructures for: Electron transport/ superconductivity? Resilience to heat, light, electric/magnetic fields? Targeted drug delivery systems? Quantum Mechanics makes it impossible to observe directly microscopic, fast atomic-scale processes Our only hope are Computer Simulations System evolution on the adiabatic surface of an electronically excited state To follow right adiabatic surfaces of excited states is rather difficult e> Potential Non adiabatic decay (finite lifetime) g> Reaction coordinate Challenges: Perform Molecular Dynamics simulations on the adiabatic surface of an electronically excited state Solve the time-dependent Schrödinger equation for electrons during ionic motion First-Principles Simulation tool for Electron-Ion Dynamics Sugino & Miyamoto PRB 59, 2579 (1999); PRB 66, (2002). 4

5 Computational Approaches Electronic structure calculations based on the ab initio Density Functional formalism Atomic motion in the electronic ground state: Molecular dynamics simulations Forces from total energy expressions: E tot = E tot ({R i }) = E tot {ρ(r)} ab initio Density Functional formalism E tot = Σ i E coh (i) = Σ i [E bs (i) + E rep (i) ] parametrized LCAO formalism (CRT) Dynamics of atoms and electrons under electronic excitations: Time-Dependent Density Functional formalism Massively parallel computer architectures and suitable algorithms distribute load over processors for speed-up State of the art computer simulations: Where are we now? 10 Petaflop 1 Petaflop 100 Teraflop 10 Teraflop 1 Teraflop Nano-materials (~1M atoms) Periodic systems (~10k atoms)? Nano-composites (~100M atoms) Nano-systems (~1B atoms) BlueGene, Earth Simulator,.. We Are Here

6 Computational Nanotechnology Laboratory: Earth Simulator, Tokyo Outline Introduction - Pioneers of nanotechnology: Carbon fullerenes and nanotubes - Challenging problems: Microscopic processes in nanostructures - State of the art of computer simulations: Where are we now? Searching High-Dimensional Phase Spaces - Fusion of fullerenes in peapods - Fusion of nanotubes Molecular Dynamics Simulations in Engineering - High thermal conductivity of nanotubes - Defect tolerance of nanotubes at high temperatures Molecular Dynamics Simulations in Medicine - Designer targeted drug delivery systems Excited State Molecular Dynamics Simulations - Light-induced self-healing of defective nanotubes - Light-induced deoxidation of nanotubes Summary and Conclusions Review: David Tománek, Carbon-based nanotechnology on a supercomputer, Topical Review in J. Phys.: Condens. Matter 17, R413-R459 (2005).

7 Searching High-Dimensional Phase Spaces Fusion of fullerenes in peapods T=1,100ºC [S. Bandow, M. Takizawa, K. Hirahara, M. Yudasaka, and S. Iijima, Chem. Phys. Lett. 337, 48 (2001)] Stone-Wales rearrangement pathway for fusion of fullerenes [Hiroshi Ueno, Shuichi Osawa, Eiji Osawa, and Kazuo Takeuchi, Fullerene Science And Technology 6, (1998) ] Stone-Wales transformation Do we understand the energetics? Sequence of bond rotations: Solve 15x15x15 Rubik s Cube puzzle

8 Do we understand the Stone-Wales process? E 2C 60 C 120 Multi-step process Search in 360-dimensional configuration space using string method: Stone-Wales is a multi-step process Activation barriers do not exceed 5eV Minimum energy path for the 2C 60 C 120 fusion Sequence of Stone-Wales transformations 2C 60 C 120 E Conclusions: -Fusion is exothermic. Energy gain ΔE 1Ry. -Essential initial step: (2+2) cycloaddition Seungwu Han, Mina Yoon, Savas Berber, Noah Park, Eiji Osawa, Jisoon Ihm, and David Tománek, Microscopic Mechanism of Fullerene Fusion, Phys. Rev. B 70, (2004).

9 Fusion of nanotubes Atomic welding with the zipper mechanism M. Yoon, S. Han, G. Kim, S. Lee, S. Berber, E. Osawa, J. Ihm, M. Terrones, F. Banhart, J.-C. Charlier, N. Grobert, H. Terrones, P. M. Ajayan, D. Tománek, Phys. Rev. Lett. 92, (2004). Zipper Minimum energy path for the (5,5)+(5,5) (10,10) fusion Sequence of Stone-Wales transformations Conclusion: Fusion is exothermic

10 Geometry of fusing Nanopants front view top view Type A: 6 heptagons in junction area Type B: 1 octagon, 4 heptagons in junction area Outline Introduction - Pioneers of nanotechnology: Carbon fullerenes and nanotubes - Challenging problems: Microscopic processes in nanostructures - State of the art of computer simulations: Where are we now? Searching High-Dimensional Phase Spaces - Fusion of fullerenes in peapods - Fusion of nanotubes Molecular Dynamics Simulations in Engineering - High thermal conductivity of nanotubes - Defect tolerance of nanotubes at high temperatures Molecular Dynamics Simulations in Medicine - Designer targeted drug delivery systems Excited State Molecular Dynamics Simulations - Light-induced self-healing of defective nanotubes - Light-induced deoxidation of nanotubes Summary and Conclusions Review: David Tománek, Carbon-based nanotechnology on a supercomputer, Topical Review in J. Phys.: Condens. Matter 17, R413-R459 (2005).

11 Molecular Dynamics Simulations in Engineering High thermal conductivity of nanotubes Savas Berber, Young-Kyun Kwon, and David Tománek, Phys. Rev. Lett. 84, 4613 (2000) Nanotubes may help solve the heat problem: Efficient conductors of electrons and heat Record Heat Conductivity: * Diamond (isotopically pure): 3320 W/m/K * Nanotubes: 6,600 W/m/K (theory, SWNT) >3,000 W/m/K (experiment, MWNT) (room temperature values) (combination of large phonon mean free path, speed of sound, hard optical phonon modes) Direct molecular dynamics simulation J S T = κ x Fourier s law J: Heat flux S: Cross section area κ: Thermal conductivity κ phonon mean free path λ (distance that phonons travel without scattering) -Q +Q Problem: Hot-cold spot separation > λ to avoid artifacts How large is λ?

12 CPU resources for a large-scale simulation One time step in MD N (number of atoms) Thermal flux propagation time along unit cell (unit cell length) N Total CPU time N Processors / 2.5 Teraflops CPU Time for L 1 : 2.5days Simulation time: 60ps N 25,000 L 2 : 10 days 120ps N 50,000 L 3 : 40 days 240ps N 100,000 (Parametrized LCAO MD calculations) Syogo Tejima et al. (in preparation) Defect tolerance of nanotubes at high temperatures Nanotube Field Effect Transistor Nanotube Defects limit performance, lifetime of devices Are CNT devices as sensitive to defects as Si-LSI circuits? atomic vacancy Will atomic vacancies trigger failure under high temperatures?

13 Stability of defective tubes at high temperatures Danger of pre-melting near vacancies? vacancy T= 0 K T= 4,000 K Nanotube remains intact until 4,000 K Self-healing behavior: Formation of new bond helps recover structural stiffness conductance Reconstructed geometry C 2 C 1 C3 Stability increase due to reconstruction (bond formation across vacancy) Does reconstruction affect favorably transport in defective tubes?

14 Quantum conductance of a (10,10) nanotube with a single vacancy Perfect tube Defective tube Choi, Ihm, Louie, Cohen, PRL (2000) Missing network of π electrons Dangling bonds: σ electrons Good news for applications: Self-healing by reconstruction may remove one of the sharp dips Outline Introduction - Pioneers of nanotechnology: Carbon fullerenes and nanotubes - Challenging problems: Microscopic processes in nanostructures - State of the art of computer simulations: Where are we now? Searching High-Dimensional Phase Spaces - Fusion of fullerenes in peapods - Fusion of nanotubes Molecular Dynamics Simulations in Engineering - High thermal conductivity of nanotubes - Defect tolerance of nanotubes at high temperatures Molecular Dynamics Simulations in Medicine - Designer targeted drug delivery systems Excited State Molecular Dynamics Simulations - Light-induced self-healing of defective nanotubes - Light-induced deoxidation of nanotubes Summary and Conclusions Review: David Tománek, Carbon-based nanotechnology on a supercomputer, Topical Review in J. Phys.: Condens. Matter 17, R413-R459 (2005).

15 Molecular Dynamics Simulations in Medicine Designer targeted drug delivery systems H cancer tumor Can we target medication delivery? Mina Yoon, Peter Borrmann, and David Tomanek, Targeted medication delivery using magnetic nanostructures (submitted for publication). Targeted Medication Delivery Inhomogeneous H Transport of inert capsule Large Homogenous H + Medication delivery How to deliver the active substance? Stability of system? H 0 H>>0

16 Structural transitions in ferrofluids H = 0 compact entangled rings H>> Time steps (msec) separated, aligned chains Mina Yoon and David Tománek, Equilibrium Structure of Ferrofluid Aggregates (submitted for publication). Thermal stability of the system Need to prevent accidental delivery! H=0 37 C T increased No accidental delivery before patient burns

17 H=1500 Oe : H<H NMR 10,000 Oe 37 C T increases Chain structure maintained at temperatures below heat stroke Outline Introduction - Pioneers of nanotechnology: Carbon fullerenes and nanotubes - Challenging problems: Microscopic processes in nanostructures - State of the art of computer simulations: Where are we now? Searching High-Dimensional Phase Spaces - Fusion of fullerenes in peapods - Fusion of nanotubes Molecular Dynamics Simulations in Engineering - High thermal conductivity of nanotubes - Defect tolerance of nanotubes at high temperatures Molecular Dynamics Simulations in Medicine - Designer targeted drug delivery systems Excited State Molecular Dynamics Simulations - Light-induced self-healing of defective nanotubes - Light-induced deoxidation of nanotubes Summary and Conclusions Review: David Tománek, Carbon-based nanotechnology on a supercomputer, Topical Review in J. Phys.: Condens. Matter 17, R413-R459 (2005).

18 Light-induced self-healing of defective nanotubes excited state vacancy e- vacancy transport hν eeground state Can atomic vacancies be healed by photo-excitations? Optical excitation (ΔE=0.9 ev) (3,3) 2nd LU electron HO hole 18

19 Time evolution of the electronic states 0 fs 70 fs Ψ n (t+δt)=exp(-i/h HΔt ) Ψ n (t) Very long-lived excitation Correct PES is followed in case of level alternation Structural changes under illumination 0 fs vacancy 190 fs new bond Self-healing due to new bond formation Y. Miyamoto, S. Berber, M. Yoon, A. Rubio, D. Tománek, Can Photo Excitations Heal Defects in Carbon Nanotubes? Chem. Phys. Lett. 392, (2004)

20 Light-induced deoxidation of nanotubes How to deoxidize? By heat treatment? No: Larger damage to nanotube By chemical treatment with H? H O Yoshiyuki Miyamoto, Noboru Jinbo, Hisashi Nakamura, Angel Rubio, and David Tománek, Photosurgical Deoxidation of Nanotubes, Phys. Rev. B 70 (2004). Alternative to thermal and chemical treatment Electronic excitations! O O-related electronic levels O2s O2p

21 O2s O2p excitation (33 ev) hopeless O2p C.B. CNT V.B. O2s Auger decay following the O1s 2p excitation (~520 ev) O2p H2 C.B. CNT V.B. 30 fs O2s 126 fs O1s 60 fs Deoxidation by photo-surgery 21

22 Seventh International Conference on the Science and Application of Nanotubes URL: or: Hotel Metropolitan Nagano Nagano, Japan June 18-23, 2006 Satellite meetings: Theory for Nanotubes (TNT 06) Drug Delivery Systems (?) Summary and Conclusions Fusion of fullerenes inside a nanotube starts with a cycloaddition and continues exclusively with Stone-Wales transformations. Fusion of nanotubes occurs efficiently via a zipper mechanism. Carbon nanotubes are Nature s best thermal conductors. Heat and photo-excitations may induce self-healing behavior in defective nanotubes. Photo-excitations can be used to selectively remove oxygen impurities. Targeted medication delivery may be induced by structural transitions in finite-size magnetic aggregates.

23 The End