Statistical Thermodynamics & Molecular Simulations (STMS) Seminar Series
These seminar series are aimed at providing a virtual platform for sharing scientific research in the area of statistical mechanics, molecular simulations, and computational materials science. In recent months, the coronavirus pandemic has stopped all large in-person scientific gatherings, including conferences and department seminars, and it is not clear that the situation will improve any time soon. STMS is aimed at filling this gap, and provide a venue for dissemination of research findings and exchange of ideas in the age of COVID. This model is being currently used by several other scientific communities, and can potentially continue even beyond the pandemic if successful.
Each seminar will be a 60-minute event and will comprise of a long-form (30-minute) talk by a principal investigator or a senior research scientists from academia or industry and a short-form (15-minute) presentation by a graduate student or a postdoc. The remainder of the event will be dedicated to Q&A (10 minutes for the PI, 5 minutes for the student/postdoc). Long-form speakers will be chosen by the STMS Organizing Committee, while we encourage suggestions from the community at large. Student and postdoctoral speakers, however, need to be nominated by their advisors. Seminars will take place on Fridays, from 11 AM-12 PM. During 2020, we expect to hold one seminar per month. The dates and the frequency of seminars for 2021 will be decided soon.
This event's talks:
Challenging the obvious answer for three different questions concerning electrolytes, nucleation and the Young-Laplace equation
Prof. Carlos Vega (Universidad Complutense de Madrid, Spain)
Abstract: The covid-19 is certainly challenging our understanding of the world and of our life so that one feels that it is a good time to think.In this presentation I will challenge three apparently "obvious" answers to three simple questions:
Question 1: Should we use integer charges (in electron units) when simulating electrolytes in water?
Obvious answer: Yes.
Question 2: Is the system at the top of a free energy barrier as found in nucleation studies identical to an equilibrium system?
Obvious answer: No.
Question 3: Is the pressure inside a spherical solid cluster higher than that of the external fluid as stated by the Young-Laplace equation?
Obvious answer: Yes
I will present some evidence that sometimes the obvious answer may not be correct[1-4].
[1] I.M. Zeron, J.L.F. Abascal, C Vega, J. Chem. Phys., 151, 134505 (2019).
[2] C.Vega, Mol. Phys., 113, 1145 (2015).
[3] P. Montero de Hijes, J. R. Espinosa, V. Bianco, E. Sanz, C.Vega, J. Phys. Chem. C, 124, 8795 (2020).
[4] P. Montero de Hijes, K. Shi, E.G. Noya, E.E. Santiso, K.E. Gubbins, E. Sanz, C. Vega, J. Chem. Phys., 153, 191102 (2020).
Can we define a unique microscopic pressure in inhomogeneous fluids?
Dr. Kaihang Shi (Northwestern University)
ABstract: The estimation of the microscopic pressure tensor in an adsorbed thin film on a planar surface remains a challenge in both experiment and theory. While the normal pressure is well-defined for a planar surface, the tangential pressure parallel to the surface at a point is not uniquely defined at the nanoscale. We show that by integrating the local tangential pressure over a small region of space, roughly the range of the intermolecular forces, it is possible to define a coarse-grained tangential pressure that is unique and free from ambiguities in the definition of the ‘virial-route’ local pressure tensor. By defining the coarse-grained tangential pressure, we can also find the effective thickness of the adsorbed layer and, in the case of a porous material, the unique pore width, which is found comparable to the internal pore width. The unique in-layer and in-pore tangential pressure are determined for Lennard-Jones argon adsorbed in carbon slit pores, providing a better understanding of the pressure enhancement for strongly wetting systems. This unequivocal definition of the microscopic pressure and the corresponding length scale will help establish a thermodynamically consistent description of highly inhomogeneous systems, and bridge the gap between experiment and theory in comparing microscopic properties.
Speaker Bio: Kaihang Shi received a B.S. (2015) in Polymer Materials and Engineering from East China University of Science & Technology (Shanghai, China). He focused on the statistical mechanics of thin adsorbed films on solid substrates and in nano-porous materials for a Ph.D. (2020) with Keith Gubbins and Erik Santiso at North Carolina State University. Kaihang has received awards acknowledging his teaching and research, including Praxair Exceptional Teaching Assistant Award, Mentored Teaching Fellowships, FOMMS poster prize, and AIChE’s CoMSEF Graduate Student Award. Kaihang is now a postdoctoral fellow at the Northwestern University with Randy Snurr.