I started my Ph. D. studies in Jan. 2009 in Stockholm University. In my Ph. D. studies, I mainly worked on numerical algorithm development and implementation of electrostatic interactions in coarse-grained simulations. After I defended my thesis in Sep. 2013, I started my postdoc research on modelling of ionic liquids. In 2016, I got a four-year fellowship from K&A Wallenberg Foundation working on multiscale modelling of structural and dynamical heterogeneities of ionic fluids in Stanford University and Stockholm University.
My current research interests include multiscale modelling of polymeric ionic fluids, algorithm development and numerical equilibrium and non-equilibrium simulations of charged soft matter systems, and computational study of luminescent properties of transition-metal complexes in biological systems.
Multiscale Modelling of Structural and Dynamical Heterogeneities of Ionic Fluids. Knut and Alice Wallenberg Foundation (KAW), 2016.10-2020.09.
I urval från Stockholms universitets publikationsdatabas
How Molecular Chiralities of Bis(mandelato)borate Anions Affect Their Binding Structures With Alkali Metal Ions and Microstructural Properties in Tetraalkylphosphonium Ionic Liquids
2020. Han-Wen Pei (et al.). Frontiers in Chemistry 8Artikel
Spiroborate anion-based inorganic electrolytes and ionic liquids (ILs) have fascinating electrochemical and tribological properties and have received widespread attention in industrial applications. The molecular chiralities of spiroborate anions have a significant effect on the microstructures and macroscopic functionalities of these ionic materials in application and thus deserve fundamental consideration. In the current work, we performed quantum chemistry calculations to address the binding strength and coordination structures of chiral bis(mandelato)borate ([BMB]) anions with representative alkali metal ions, as well as the electronic properties of alkali metal ion-[BMB] ion pair complexes. The optimized [BMB] conformers are categorized into V-shaped, bent, and twisted structures with varied electrostatic potential contours and conformational energies and distinct alkali metal ion-[BMB] binding structures. Alkali metal ions have additional associations with phenyl groups in V-shaped [BMB] conformers owing to preferential cation-pi interactions. Furthermore, the effects of the molecular chiralities of [BMB] anions on the thermodynamics and microstructural properties of tetraalkylphosphonium [BMB] ILs were studied by performing extensive atomistic interactions. Oxygen atoms in [BMB] anions have competitive hydrogen bonding interactions with hydrogen atoms in cations depending on the molecular chiralities and steric hindrance effects of [BMB] anions. However, the molecular chiralities of [BMB] anions have a negligible effect on the liquid densities of tetraalkylphosphonium [BMB] ILs and the spatial distributions of boron atoms in anions around phosphorous atoms in cations. Enlarging tetraalkylphosphonium cation sizes leads to enhanced cation-anion intermolecular hydrogen bonding and Coulombic interactions due to enhanced segregation of polar groups in apolar networks in heterogeneous IL matrices, as verified by scattering structural functions.
Imidazole and 1-Methylimidazole Hydrogen Bonding and Nonhydrogen Bonding Liquid Dynamics
2019. Jae Yoon Shin (et al.). Journal of Physical Chemistry B 123 (9), 2094-2105Artikel
The dynamics of imidazole (IM) and 1-methylimidazole (1-MeIM) in the liquid phase at 95 degrees C were studied by IR polarization selective pump-probe and two-dimensional IR (2D IR) spectroscopies. The two molecules are very similar structurally except that IM can be simultaneously a hydrogen bond donor and acceptor and therefore forms extended hydrogen-bonded networks. The broader IR absorption spectrum and a shorter vibrational lifetime of the vibrational probe, selenocyanate anion (SeCN-), in IM vs 1-MeIM indicate that stronger hydrogen bonding exists between SeCN- and IM. Molecular dynamics (MD) simulations support the strong hydrogen bond formation between SeCN- and IM via the HN moiety. SeCN- makes two H-bonds with IM; it is inserted in the IM H-bonded chains rather than being a chain terminator. The strong hydrogen bonding influenced the reorientation dynamics of SeCN- in IM, leading to a more restricted short time angular sampling (wobbling-in-a-cone). The complete orientational diffusion time in IM is 1.7 times slower than in 1-MeIM, but the slow down is less than expected, considering the 3-fold larger viscosity of IM. The jump reorientation mechanism accounts for the anomalously fast orientational relaxation in IM, and the MD simulations determined the average jump angle of the probe between hydrogen bonding sites. Spectral diffusion time constants obtained from the 2D IR experiments are only modestly slower in IM than in 1-MeIM in spite of the significant increase in viscosity. The results indicate that the spectral diffusion sensed by the SeCN- has IM hydrogen bond dynamics contributions not present in 1-MeIM.
Poly(Ionic Liquid)-Derived Graphitic Nanoporous Carbon Membrane Enables Superior Supercapacitive Energy Storage
2019. Weiyi Zhang (et al.). ACS Nano 13 (9), 10261-10271Artikel
High energy/power density, capacitance, and long-life cycles are urgently demanded for energy storage electrodes. Porous carbons as benchmark commercial electrode materials are underscored by their (electro)chemical stability and wide accessibility, yet are often constrained by moderate performances associated with their powdery status. Here via controlled vacuum pyrolysis of a poly(ionic liquid) membrane template, advantageous features including good conductivity (132 S cm(-1) at 298 K), interconnected hierarchical pores, large specific surface area (1501 m(2) g(-1)), and heteroatom doping are realized in a single carbon membrane electrode. The structure synergy at multiple length scales enables large areal capacitances both for a basic aqueous electrolyte (3.1 F cm(-2)) and for a symmetric all-solid-state supercapacitor (1.0 F cm(-2)), together with superior energy densities (1.72 and 0.14 mW h cm(-2), respectively) without employing a current collector. In addition, theoretical calculations verify a synergistic heteroatom co-doping effect beneficial to the supercapacitive performance. This membrane electrode is scalable and compatible for device fabrication, highlighting the great promise of a poly(ionic liquid) for designing graphitic nanoporous carbon membranes in advanced energy storage.
Atomistic Insight into Orthoborate-Based Ionic Liquids
2014. Yong-Lei Wang (et al.). Journal of Physical Chemistry B 118 (29), 8711-8723Artikel
We have developed an all-atomistic force field for a new class of halogen-free chelated orthoborate-phosphonium ionic liquids. The force field is based on an AMBER framework with determination of force field parameters for phosphorus and boron atoms, as well as refinement of several available parameters. The bond and angle force constants were adjusted to fit vibration frequency data derived from both experimental measurements and ab initio calculations. The force field parameters for several dihedral angles were obtained by fitting torsion energy profiles deduced from ab initio calculations. To validate the proposed force field parameters, atomistic simulations were performed for 12 ionic liquids consisting of tetraalkylphosphonium cations and chelated orthoborate anions. The predicted densities for neat ionic liquids and the [P-6,P-6,P-6,P-14][BOB] sample, with a water content of approximately 2.3-2.5 wt %, are in excellent agreement with available experimental data. The potential energy components of 12 ionic liquids were discussed in detail. The radial distribution functions and spatial distribution functions were analyzed and visualized to probe the microscopic ionic structures of these ionic liquids. There are mainly four high-probability regions of chelated orthoborate anions distributed around tetraalkylphosphonium cations in the first solvation shell, and such probability distribution functions are strongly influenced by the size of anions.
Implementation of non-uniform FFT based Ewald summation in dissipative particle dynamics method
2013. Yong-Lei Wang, Aattoo Laaksonen, Zhong-Yuan Lu. Journal of Computational Physics 235, 666-682Artikel
The ENUF method, i.e., Ewald summation based on the non-uniform FFT technique (NFFT), is implemented in dissipative particle dynamics (DPD) simulation scheme to fast and accurately calculate the electrostatic interactions at mesoscopic level. In a simple model electrolyte system, the suitable ENUF–DPD parameters, including the convergence parameter α, the NFFT approximation parameter p, and the cut-offs for real and reciprocal space contributions, are carefully determined. With these optimized parameters, the ENUF–DPD method shows excellent efficiency and scales as O(NlogN)O(NlogN). The ENUF–DPD method is further validated by investigating the effects of charge fraction of polyelectrolyte, ionic strength and counterion valency of added salts on polyelectrolyte conformations. The simulations in this paper, together with a separately published work of dendrimer–membrane complexes, show that the ENUF–DPD method is very robust and can be used to study charged complex systems at mesoscopic level.
Multiscale coarse-grained simulations of ionic liquids
2013. Yong-Lei Wang (et al.). Physical Chemistry, Chemical Physics - PCCP 15 (20), 7701-7712Artikel
A coarse-grained model, with three sets of effective pair potentials for 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) ionic liquid, is introduced and used to study the structural and dynamical properties over extended length and time scales. Three sets of effective pair potentials between coarse-grained beads are obtained using the Newton Inversion and the Iterative Boltzmann Inversion methods, respectively, with different treatment of electrostatic interactions. The coarse-grained simulation results are compared systematically with corresponding atomistic simulation results on several thermodynamical and structural quantities together with charge density distributions. In addition, the scattering and dynamical properties are also calculated and compared to both atomistic simulation results and experimental measurements. While all three sets of the effective potentials provide perfect agreement with the atomistic simulation for radial distribution functions, our analysis shows that in coarse-grained simulations, the long-range electrostatic interactions between ionic groups are important and should be treated explicitly to improve the reliability of other simulation results. With explicit incorporation of electrostatic interactions derived from the Newton Inversion, the coarse-grained potentials provide the most consistent description of thermodynamical, scattering and dynamical properties including their temperature dependence as compared to atomistic simulations. We conclude also that the current atomistic force field should be further improved to meet specific requirements for studying the dynamical properties of the [Bmim][PF6] system over a large temperature range.