Seminarium IF – Dr Erik Santiso

seminarium Instytutu Fizyki – 9 lipca, godz. 12.30

Wykład pod tytułem „ Molecular Modeling of Nucleation of Organic Crystals”

wygłosił

Dr. Erik Santiso
Department of Chemical and Biomolecular Engineering, North Carolina State University

 

Introduction

Crystallization of organic molecules is central to applications ranging from drug manufacturing and food processing to optical and energetic materials. However, the study of molecular crystal nucleation remains challenging for both experimental and computational approaches. The stochastic nature of nucleation and its sensitivity to defects and impurities complicate reproducible measurements. On the simulation side, nucleation is a rare event with low transmission coefficient, requiring advanced enhanced sampling approaches, and competing mechanisms such as classical vs. two-step nucleation are possible. Furthermore, finite size artifacts often cause spurious results, appropriate force fields are often unavailable, and simulated systems are too idealized to meaningfully compare to experiment.

We address some of these difficulties through an approach that maps minimum free energy pathways for nucleation using the string method in collective variables with collective variables derived from the crystal structure. This approach has been applied to nucleation from both melts and solutions for systems such as ionic liquids and sulfonamide drugs. More recently, we have extended our method to fit collective variables to local liquid structure, including solvent degrees of freedom into the reaction coordinate. These parameters signal the likelihood of one-step vs. two-step mechanisms, and enable quantitative assessment of the effect of solvent structure around the incipient nucleus. These order parameters are available in PLUMED (v2.9 and later), facilitating broader use in enhanced-sampling simulations. Finally, we introduce a layer-by-layer order-parameter construction that tracks the growth of the nucleus and opens the door to mechanistic studies of more complex crystals, including solvates and cocrystals.

Bio: Erik Santiso received his Bachelor’s and Master’s degrees in Chemical Engineering at Universidad Simón Bolivar in Caracas, Venezuela, and obtained his Ph.D. in Chemical Engineering at North Carolina State University in 2007. He then worked as a postdoctoral associate at MIT and Imperial College London, and joined the faculty at NC State University in 2013, where he currently works as an Associate Professor in the Department of Chemical and Biomolecular Engineering. His interests include the modeling of complex activated processes such as nucleation and chemical reactions in solution, developing models to predict the structure and properties of peptoids, thermodynamics of confined systems, and using hybrid coarse-graining methods to build polymer models.