Chao Zhang

Associate senior lecturer/Assistant Professor at Department of Chemistry - Ångström Laboratory, Structural Chemistry

Email:
chao.zhang[AT-sign]kemi.uu.se
Telephone:
+4618-471 3721
Visiting address:
Lägerhyddsvägen 1

Postal address:
Box 538
751 21 Uppsala

Short presentation

According to the two-volume "Modern Electrochemistry" written by Bockris and Reddy, there are two kinds of electrochemistry. The first one is "The physical chemistry of ionically conducting solutions" and the second one is "The physical chemistry of electrically charged interfaces". We are working on the fundamental side of these topics in energy storage/conversion applications.

Drop me a line if you are interested in a thesis work (Master/PhD) or a research project (Postdoc).

Keywords: density functional theory molecular dynamics solid state batteries electrolytes charged water interfaces atomistic machine learning

Prelude

A respectable senior colleague once told me that a person doing Computational Electrochemistry needs to know four things (five to include Machine Learning): electronic structure theory, statistical mechanics, classical electrodynamics and chemical thermodynamics. This puts the density functional theory based molecular dynamics (DFTMD) as the method of choice. To me, DFTMD is not just a method but a spirit (or a bridge) which connects the "hard" world (solid state/surface science community) and "soft" world (soft matter/liquid state theory community).

Modelling electrochemical interfaces with finite field MD

A realistic representation of an electrochemical interface requires treating electronic, structural and dynamic properties on an equal footing. DFTMD method is perhaps the only approach that can provide a consistent atomistic description. However, the challenge for DFTMD modelling of material’s interfacial dielectrics is the slow convergence of the polarization P, where P is a central quantity to connect all dielectric properties of an interface.

Our contribution is to develop finite field MD simulation techniques for computing electrical properties (such as the dielectric constant of polar liquids and the Helmholtz capacitance of solid-electrolyte interfaces) [1, 2]. Its DFTMD implementation is available in one of our community codes CP2K (www.cp2k.org).

Simulating charge transportation in battery electrolytes

Lithium batteries are electrochemical devices which involve multiple time-scale and length-scale to achieve its optimal performance and safety requirement. In terms of the electrolyte which serves as the ionic conductor, a molecular-level understanding of the corresponding transport phenomenon is crucial for the rational design.

Currently, we are working on MD simulations of ionic conductivities in different types of electrolytes from aqueous electrolytes to polymer electrolytes (with Daniel Brandell) which are relevant to battery applications [3,4].

Developing atomistic machine learning for materials modelling

Machine learning (ML) is becoming increasingly important in computational chemistry and materials discovery. Atomic neural networks (ANN), which constitute a class of ML methods, have been very successful in predicting physico-chemical properties and approximating potential energy surfaces.

Recently, we have taken the initiative and developed an open-source Python library named PiNN (https://github.com/Teoroo-CMC/PiNN/), allowing researchers to easily develop and train state-of-the-art ANN architectures specifically for making chemical predictions. In particular, we have designed and implemented an interpretable and high-performing graph convolutional neural network architecture PiNet [5,6], and demonstrate how the chemical insight “learned” by such a network can be extracted.

[1] Zhang, C., Hutter, J. and Sprik, M. J. Phys. Chem. Lett., 2019, 10: 3871, DOI:10.1021/acs.jpclett.9b01355

[2] Zhang, C., Sayer. T., Hutter, J. and Sprik, M. J. Phys.: Energy, 2020, 2: 032005, DOI:10.1088/2515-7655/ab9d8c (Topical Review)

[3] Shao, Y., Hellström, M., Yllö A., Mindemark, J., Hermansson, K., Behler, J. and Zhang, C. Phys. Chem. Chem. Phys., 2020, 22: 10426, DOI: 10.1039/C9CP06479F (2020 HOT PCCP article)

[4] Gudla, H., Zhang, C. and Brandell, D. J. Phys. Chem. B, 2020, 124: 8124, DOI: 10.1021/acs.jpcb.0c05108

[5] Shao, Y., Hellström, M., Mitev, P. D., Knijff, L. and Zhang, C. J. Chem. Inf. Model., 2020, 60: 1184, DOI: 10.1021/acs.jcim.9b00994

[6] Shao, Y., Knijff, L., Dietrich, F. M., Hermansson, K. and Zhang, C. Batter. Supercaps, 2021, DOI:10.1002/batt.202000262 (Minireview)

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Chao Zhang