Check here for the latest happenings in the group.
Andrew Paluch successfully passed his PhD defense. In the fall he will join the Department of Chemical and Paper Engineering at Miami University as an assistant professor. Congratulations Andrew!
Marcos Perez-Blanco successfully passed his PhD thesis defense. He will go on to work as a programmer at Epic in Madison, WI. Congratulations Marcos!
Yong's paper entitled "Toward Fully in Silico Melting Point Prediction Using Molecular Simulations" just appeared in the Journal of Chemical Theory and Computation (2013, 9(3), 1592-1599). In this paper, he shows how crystal structure prediction methods can be combined with the "pseudosupercritical path sampling" approach for determining the free energy between crystalline and liquid phases to predict melting points with no recourse to experimental data. The method is applied to two test molecules 2-propenal and 4-cyanopyridine N-oxide. The method works well for these molecules, even if the predictd crystal structures do not math the experimental ones. Thsi is due to the closeness in free energies of the predicted and actual crystal structures. The method did not work well for it was applied to the more complex molecule 6-amino-2-(phenylsulfonylimino)-1,2-dihydrophridine. We suspect this is due to limitations on the force field. This is exciting work, and we hope it can be generalized to many more compounds.
Yong Zhang published a paper entitled "The Effect of C2 Substitution on Melting Points and Liquid Phase Dynamics of Imidazolium-Based Ionic Liquids: Insights from Molecular Dynamics Simulations”, in Physical Chemistry Chemical Physics, 2012, 14(35), 12157-12164. In it, he provided detailed evidence that entropic effects play a big role in determining the melting point and viscosity trends observed when the C2 carbon of imidazolium-based ionic liquids is methylated.
The origin of higher melting points of C2 methylated alkyl-imidazolium PF6 ionic liquids is mainly entropic.
Andrew Paluch, Cameron Vitter and Jindal Shah published a paper entitled “A Comparison of the Solvation Thermodynamics of Amino Acid Analogues in Water, 1-Octanol and 1-n-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide Ionic Liquids by Molecular Simulation”, in Journal of Chemical Physics, 2012, 137, 184505. They developed a "hydrophobicity scale" and showed how expanded ensemble simulations can be used to quantitatively estimate the solvation thermodynamics of amino acid analogues in various solvents, including ionic liquids.
A comparison of the dimensionless molar entropy of transfer between solvent A and water, and lnK* computed at 328 K via molecular simulation. Solvent A corresponds to either 1-octanol, [emim]+ [Tf2 N]− , [bmim]+ [Tf2 N]− , [omim]+ [Tf2 N]− , or p-octanol, as indicated by the leg- end.
Welcome to Quintin Sheridan and Brian Yoo, the two most recent PhD students to join the group. Quintin is jointly working with Prof. Maginn and Prof. Schneider on a GCEP-funded project looking at the development of ionic liquids for pre-combustion CO2 capture. Brian is working jointly with Prof. Maginn and Prof. Zhu on an NSF-sponsored project focused on understanding the mechanistic details associated with the toxicity of ionic liquids. Welcome Quintin and Brian!
Dr. Sandip Khan has joined the group, and will be working on simulations of solid solutions of mixed oxides as part of the Materials Science of Actinides EFRC project. Sandip received his PhD in chemcial engineering from the Indian Institute of Technology, Kanpur under the direction of Prof. Jayant Singh. Welcome, Sandip!
Yong Zhang has published a paper ("A Simple AIMD Approach to Derive Atomic Charges for Condensed Phase Simulation of Ionic Liquids”, Journal of Physical Chemistry B, 2012, 116, 10036-10048) showing how partial charges can be obtained for ionic liquids using ab initio methods. More accurate results are obtained when the charges are derived from condensed phase simulations, but sampling liquid configurations is very time consuming. Yong shows in this work that accurate charges can be obtained from simulations of the crystalline phase, thereby saving a huge amount of time. Interestingly, properties such a diffusivity and melting point are more accurately modeled using the charges derived in this way than if other approaches are used.
Neeraj Rai and Surya Tiwari published a paper (Force Field Development for Actinyl Ions via Quantum Mechanical Calculations: An Approach to Account for Many Body Solvation Effects”, Journal of Physical Chemistry B, 2012, 116, 10885-10897) in which they showed how to develop a simple yet accurate pair potential for uranyl ions in water. Their approach uses explicitly solvated UO22+ ions along with MP2 energy scans to generate potential energy surfaces. These are then fit to a force field consisting of Lennard-Jones + partial charge terms. Condensed phase simulations show that the force field faithfully reproduces experimental liquid structure and solvation free energies.
Dr. Yong Zhang published a paper entitled "The Effect of C2 Substitution on Melting Points and Liquid Phase Dynamics of Imidazolium-Based Ionic Liquids: Insights from Molecular Dynamics Simulations”, in Physical Chemistry Chemical Physics, 2012, 14(35), 12157-12164. In this paper, he shows that entropic effects are a major reason why adding a methyl group to the C2 position of an imidazolium ring increases melting points and viscosities. Congratulations, Yong.