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 1 st Workshop on HPC in SC-09

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-092 Current Challenge Vesicle interacting with a lipid membrane Shinoda and Klein, Science (2008) ‏

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-093 Molecular dynamics Obtain Forces, Integrate tt

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-094 Parallelization strategies  Decomposition based on particle indices (works for < 1000 particles) ‏  Domain/Spatial decomposition (for large system sizes ~ 1 million) ‏  Decomposition based on particle indices (works for < 1000 particles) ‏  Domain/Spatial decomposition (for large system sizes ~ 1 million) ‏ System of interacting particles

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-095 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

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-096 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

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-097 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?

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-098 Multiscale Modeling Atomistic Coarse Grain Ab Initio

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-099 Ionic compounds NaCl M.P.: 801 ºC [bmim][PF 6 ] M.P.: 10 ºC  Low volatility  Environmentally benign  Polar liquids  Nanoparticle synthesis, electrolytes, catalysis

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0910 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

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0911 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)

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0912 Refined atomistic model: Predictions  Density within 1.5% of experiment between K, 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) Refining the parameters of the atomistic model to match the intermolecular structure of AIMD provides:

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0913 Intermolecular structure B.L. Bhargava, M.L. Klein and S. Balasubramanian, ChemPhysChem (2008)

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0914 Coarse graining Example: [C 7 mim][PF 6 ] 41 atoms versus 6 beads Can be used for any [C n mim][PF 6 ] Studied here: n=4, 7, 10 Parametrized for [C 4 mim][PF 6 ] 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)

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0915 Nanoscale ordering NEUTRON X-RAY [C 4 mim][PF 6 ] [C 10 mim][PF 6 ] [C 7 mim][PF 6 ] Increasing Correlation Length Triolo et al (2008) SIMULATION EXPERIMENT BLB, RD, MLK & SB, Soft Matt. (2007)

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0916 Morphology Bicontinuous 12 nm Anion Rich Tail Rich BLB, RD, MLK & SB, Soft Matt. (2007)

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0917 Symmetric tails 1-butyl,3-methylimidazolium hexafluorophosphate 1,3-didecylimidazolium hexafluorophosphate Asymmetric tails Symmetric tails Dzyuba and Bartsch Chemcomm (2001) “The didecyl compound has two melting points: -27 o C and 16 o C” Raju and Balasubramanian, J. Mater. Chem. (2009)

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0918 Emergence of lamellar phase After 50 nsAfter 450 ns Sectional View: After 450 ns Lamellar Phase Self Assembly Raju and Balasubramanian, J. Mater. Chem. (2009)

Balasubramanian Sundaram ATIP 1 st Workshop on HPC in SC-0919 Summary  D evelopment 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.