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Modelling Soft Matter

Modelling Soft Matter. Balasubramanian Sundaram Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore. ATIP 1 st Workshop on HPC in India @ SC-09. Current Challenge. Vesicle interacting with a lipid membrane.

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Modelling Soft Matter

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  1. Workshop on HPC in India Modelling Soft Matter Balasubramanian Sundaram Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore ATIP 1st Workshop on HPC in India @ SC-09

  2. ATIP 1st Workshop on HPC in India @ SC-09 Current Challenge Vesicle interacting with a lipid membrane Shinoda and Klein, Science (2008)‏

  3. ATIP 1st Workshop on HPC in India @ SC-09 Molecular dynamics Obtain Forces, Integrate t

  4. ATIP 1st Workshop on HPC in India @ SC-09 Parallelization strategies • Decomposition based on particle indices (works for < 1000 particles)‏ • Domain/Spatial decomposition (for large system sizes ~ 1 million)‏ System of interacting particles • Decomposition based on particle indices (works for < 1000 particles)‏ • Domain/Spatial decomposition (for large system sizes ~ 1 million)‏

  5. ATIP 1st Workshop on HPC in India @ SC-09 Approaches • Density functional theory based MD (ab initio molecular dynamics)‏ • Accurate, but expensive • Empirical force field based atomistic MD • Less accurate than DFT, but reasonable; not so expensive • Coarse grain MD • Softer forces, fewer degrees of freedom, ideal to study mesoscale phenomena

  6. ATIP 1st Workshop on HPC in India @ SC-09 Hierarchical modelling • Perform ab initio MD (AIMD) calculations. Obtain information on intermolecular structure • Refine empirical force-field parameters so that the results of atomistic MD match those from AIMD. • Use results of atomistic MD to carry out coarse grain simulations

  7. ATIP 1st Workshop on HPC in India @ SC-09 Challenges • Length and time scales of processes and phenomena are large (tens of nanometers, micro to milliseconds) • Atomistic description is crucial to understand the chemistry of specific substances • How does one build models starting from atomistic ones, to reach the large length/time scales?

  8. ATIP 1st Workshop on HPC in India @ SC-09 Multiscale Modeling Ab Initio Atomistic Coarse Grain

  9. ATIP 1st Workshop on HPC in India @ SC-09 Ionic compounds NaCl M.P.: 801 ºC • Low volatility • Environmentally benign • Polar liquids • Nanoparticle synthesis, electrolytes, catalysis [bmim][PF6] M.P.: 10 ºC

  10. ATIP 1st Workshop on HPC in India @ SC-09 Issues • Lack of scattering data to determine intermolecular structure in the liquid state • Transferability of intermolecular potentials whose partial charges are fitted to gas phase quantum calculations • Phase behaviour • Prediction of bulk properties • Microheterogeneity

  11. ATIP 1st Workshop on HPC in India @ SC-09 Intermolecular structure Anions come closer due to electronic polarization B.L. Bhargava and S. Balasubramanian Journal of Physical Chemistry B 111, 4477 (2007) Atomistic (non-bonded): CLP model, JPCB (2004)

  12. ATIP 1st Workshop on HPC in India @ SC-09 Refined atomistic model: Predictions Refining the parameters of the atomistic model to match the intermolecular structure of AIMD provides: • Density within 1.5% of experiment between 300-500K, within 2% up to 200 MPa • Diffusion coefficients within 20% of experiment at 300K/1atm • Surface tension at 300K within 10% of experiment • Enthalpy of vaporization within 10% of experiment B.L. Bhargava and S. Balasubramanian, J. Chem. Phys. (2007)

  13. ATIP 1st Workshop on HPC in India @ SC-09 Intermolecular structure B.L. Bhargava, M.L. Klein and S. Balasubramanian, ChemPhysChem (2008)

  14. ATIP 1st Workshop on HPC in India @ SC-09 Coarse graining • Around 3 heavy atoms per bead • Atom charges summed up to give bead charges • Atom dispersion strengths summed up to give bead Epsilons • Beads of alkyl tail: Model based on surfactants (Shinoda et al) Example: [C7mim][PF6] 41 atoms versus 6 beads Can be used for any [Cnmim][PF6] Studied here: n=4, 7, 10 Parametrized for [C4mim][PF6]

  15. ATIP 1st Workshop on HPC in India @ SC-09 Nanoscale ordering Triolo et al (2008) NEUTRON X-RAY EXPERIMENT SIMULATION [C4mim][PF6] Increasing Correlation Length [C7mim][PF6] BLB, RD, MLK & SB, Soft Matt. (2007) [C10mim][PF6]

  16. ATIP 1st Workshop on HPC in India @ SC-09 Morphology 12 nm Anion Rich Tail Rich Bicontinuous BLB, RD, MLK & SB, Soft Matt. (2007)

  17. ATIP 1st Workshop on HPC in India @ SC-09 Symmetric tails Asymmetric tails 1-butyl,3-methylimidazolium hexafluorophosphate Symmetric tails 1,3-didecylimidazolium hexafluorophosphate Dzyuba and Bartsch Chemcomm (2001) “The didecyl compound has two melting points: -27oC and 16oC” Raju and Balasubramanian, J. Mater. Chem. (2009)

  18. ATIP 1st Workshop on HPC in India @ SC-09 Emergence of lamellar phase After 50 ns After 450 ns Lamellar Phase Self Assembly Sectional View: After 450 ns Raju and Balasubramanian, J. Mater. Chem. (2009)

  19. ATIP 1st Workshop on HPC in India @ SC-09 Summary • Development of a hierarchical approach to model room temperature ionic liquids • Ab initio, atomistic and coarse grain simulations carried out • Quantitative comparison to experiments at each stage • We predict the formation of a lamellar phase in ionic liquids containing cations with symmetric long alkyl groups.

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