News

Junwei (Lucas) Bao of the Truhlar group has Junwei Lucas Baoreceived the Overend Award in Physical Chemistry. His research includes an original method for pressure-dependent rate constants in chemical kinetics, the identification of systematic methods to choose active spaces for multireference quantum mechanical calculations on transition metal chemistry by both multiconfiguration wave function methods and multiconfiguration pair-density functional theory, and the calculation of reliable rate constants for reactions important to nucleation in plasmas. His work has involved collaboration with Professor Laura Gagliardi, current or past visiting professors Annia Galano, Bo Long, Xuefei Xu, and Xin Zhang, research associates Rubén Meana-Pañeda and Jingjing Zhang, postdoctoral associates Giovanni Li Manni, Andrew Sand, and Prasenjit Seal, graduate students Kaining Duanmu, Samuel Odoh, and Haoyu Yu, and visiting graduate student Lili Zhang plus other researchers at other institutions. The work at the University of Minnesota has been funded by DOE and NSF.

Lucas began his graduate work in our department in fall 2014. He received a teaching award in 2015. He was awarded a best poster prize at the 15th International Congress of Quantum Chemistry in 2015. He was awarded the Beaker and Bunsen Award for a best presentation at the 2016 Chemistry Graduate Student Research Symposium in 2016.  He has received the John Overend Award for graduate research in physical chemistry; these fellowships are awarded on a competitive basis to the University's most accomplished Ph. D. candidates.

His work has led so far to nineteen published and accepted papers in leading journals, on 12 of which he is sole first author, and on a thirteenth of which he is flagged for contributing equally with the first author. His 13 first-author papers include one each in Proceedings of the National Academy of Sciences, Journal of the American Chemical Society (the flagship journal of the ACS), Chemical Science (the flagship journal of the Royal Society of Chemistry), and ACS Catalysis, six in Physical Chemistry Chemical Physics, and three in Journal of Chemical Theory and Computation. The other six are in ACS Energy Letters, Chemistry - A European Journal, Accounts of Chemical Research, Journal of the American Chemical Society, Advanced Energy Materials, and The Journal of Physical Chemistry A.

A failing of local Kohn-Sham exchange-correlation functionals, known since the early days [Yin, M. T.; Cohen, M. L. Theory of Static Structural Properties, Crystal Stability, and Phase Transformations: Application to Si and Ge. Phys. Bev. B 1982, 26, 5668–5687] of the application of density functional theory in physics is the significant underestimation of semiconductor band gaps, which are one of the most critical properties of materials for many applications. In order to work around this problem, researchers have developed a number of alternatives, such as the DFT+U method, which requires reparameterization for every new system, and so has limited predictive power, and nonlocal functionals, which increase the cost in plane wave codes by two to three orders of magnitude.

Now, in a major breakthrough, graduate student Pragya Verma and Professor Donald G. Truhlar have developed a local functional that corrects this problem by scaling up a local exchange functional. An article describing the new functional was published today as “HLE16: A Local Kohn–Sham Gradient Approximation with Good Performance for Semiconductor Band Gaps and Molecular Excitation Energies,” P. Verma and D. G. Truhlar, Journal of Physical Chemistry Letters 8, 380-387 (2016). dx.doi.org/10.1021/acs.jpclett.6b02757. Tested on a database of 31 semiconductor band gaps, the functional has a mean unsigned error of 0.30 eV, which compares well to the most popular nonlocal functional for band gaps, HSE06, which has a mean unsigned error of 0.31 eV. The popular local functionals PBE and BLYP have mean unsigned errors of 1.11 and 1.13 eV, respectively. The new functional, which does not require reparameterization for each new material, also shows good accuracy for molecular Rydberg states, which is another previous failing of local functionals.

ss-qrrk-newsBarrierless association reactions and bond dissociation reactions play important roles in combustion and atmospheric chemistry, as well as being of fundamental importance in the theory of chemical kinetics. Calculating their rate constants is challenging for both electronic structure theory and kinetics theory. From the electronic structure viewpoint, it is difficult to obtain a qualitatively correct potential curve in the bond-breaking region where the variational transion state is located. In a paper that appeared today in the early edition of Proceedings of the National Academy of Sciences,

   dx.doi.org/10.1073/pnas.1616208113

we validated an exchange–correlation functional against beyond-CSDT electronic structure theory, and we used the resulting density functional method for direct dynamics calculations of the pressure- dependent rate constants for the C=C bond dissociation of C2F4 by applying multifaceted variable-reaction-coordinate variational transition-state theory with the recently developed system-specific quantum Rice–Ramsperger–Kassel theory. Our computed dissociation rate constants agree well with the recent experimental measurements by Troe and coworkers. This work presents a prototypical example of the full treatment of the kinetics of barrierless reactions and their reverse reactions, including variational optimization of the transition state, multidimensional tunneling, and pressure effects. The supporting information of the article gives full details of the variable-reaction-coordinate variational transition state theory calculation of the high-pressure limiting rate constant.

We believe that the system-specific quantum RRK method employed in this work makes it much more convenient to accurately model pressure-dependent rate constants than was possible with previously available methods.

November 10, 2016

Kaining defenseOn Sept. 6, 2016, Kaining Duanmu successfully defended his thesis, making a presentation mainly focused on his work on silver clusters. The photo shows him with his committee immediately after the exam – left to right: Chris Hogan, Don Truhlar, Kaining, Laura Gagliardi, and Chris Cramer.

Kaining’s Ph. D. research included

  • water splitting on Fe(0)
  • surface defects on reconstructed α-quartz exposed to oxygen
  • geometries, structures, and energies of neutral and charged silver clusters
  • geometries, binding energies, ionization potentials, electron affinities, and enthalpies of formation of neutral and charged magnesium clusters and nanoparticles
  • size-dependent ligand quenching of ferromagnetism in superparamagnetic Co3(benzene)n+ clusters

He next moves on to a postdoctoral research position with Professor Phillippe Sautet at UCLA.

Kelsey ParkerKelsey Parker has been awarded an Excellence Fellowship by the Department of Chemistry for 2016-2017. These fellowships are established to promote and reward excellence in the department’s Graduate Program. Kelsey is working on quantum photochemistry with current emphasis on methylamine and retinal. Her first publication in our group may be accessed at dx.doi.org/10.1063/1.4948728.  Congratulations Kelsey!

PtO4Formal oxidation state is one of the most widely used identifiers for understanding the mechanisms of oxidation-reduction reactions and catalysis. Metals in high oxidation states are known to have strong catalytic properties and oxidizing power, and therefore there is intense interest in preparing species with metals in high oxidation states. Furthermore, the study of variations in oxidation state contributes to our general understanding of the periodic trends across the periodic table and to our understanding of the feasibility of various redox reactions. The reaction mechanisms and products of reactions are often determined by the oxidation state of the reactants and the possible products. The quest for higher oxidation states of transition metals is central to much current research on catalysis as well as being of fundamental importance in chemistry. The question naturally arises then of what is the highest oxidation state that might be found in nature. Previously, the range of oxidation states was -4 to +9. Now graduate student Haoyu Yu and Regents Professor Donald Truhlar have a “Hot Paper,” published in Angewandte Chemie (DOI: 10.1002/anie.201604670) that reveals that oxidation state 10 exists. This work is featured in the C&EN news and Chemistry World.

To come to this conclusion, they examined the stability of various  transition metal compounds with a metal formal oxidation state of 10 by using Kohn–Sham density functional theory, and PtO42+ was found to be stable. PtO42+ has a similar electron density but a larger partial atomic charge on the metal than one finds in IrO4+, which is the compound with the previously highest oxidation state. Note that PtO42+ and IrO4+ are isoelectronic with the commodity chemical OsO4.

Interestingly, the lowest oxidation state in nature was also determined in the Chemistry Department at the University of Minnesota, in particular by Professor John Ellis, who reported (J. Am. Chem. Soc. 1983, 105, 2296) the oxidation state of -4 for the super-reduced species Na4M(CO)4, where M can be Cr, Mo, or W in their lowest oxidation states of -4.

This work was supported as part of the Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DE-SC0012702.

June 14, 2016

Story from the Department of Chemistry News:

Regents Professor Donald Truhlar has received a 2015-16 Outstanding Advising and Mentoring Award from the Council of Graduate Students, Professional Student Government, and Student Conflict Resolution Center. This is the third consecutive year that Truhlar has received this honor.

His nomination praised his responsiveness, encouraging nature, and precision as a scientist. One of his nominators wrote: "Thanks to Professor Truhlar I am not only more confident, but also I am able to see that obtaining my goals is a combination of attitude, interest, and hard work." Another nominator wrote, "Behind this great scientist is a very generous and caring mentor." 

The Outstanding Advising and Mentoring Award award was established in 2010 as a way to recognize contributions of faculty members who go above and beyond in their work with graduate students. It is the only award where faculty members are nominated by and winners are selected by graduate students. Forty faculty members were nominated and seven were chosen to receive this award. Truhlar was honored at a recognition ceremony, Thursday, April 21. A photo of Professor Truhlar and the other winners can be seen at wbt.umn.edu.

 

overend

Shaohong Li received the 2016 Overend Award for Graduate Research in Physical Chemistry from Professor Aaron Massari today before the Moscowitz Lecture by Georg Kresse of the University of Vienna. This award is given annually to recognize an outstanding graduate student researcher in our department.  Recent recipients of this award in the Truhlar group are

  2016 Shaohong Li
  2011 Hannah Leverentz
  2010 Bo Wang
  2006 Erin Dahlke
  2003 Jingzhi Pu and Jason Thompson
  2001 Ahren Jasper
  1999 Michael D. Hack 
  1997 Yao-Yuan Chuang (Wertz Award)
  1994 Wei-Ping Hu
  1993 Steven Mielke (Wertz Award)
  1992 Yi-Ping Liu

Shaohong was honored for work on a variety of projects, including:

  • configuration-interaction-corrected Tamm-Dancoff Approximation (read more) for using time-dependent density functional theory (TDDFT) to predict conical intersections with the correct dimensionality
  • TDDFT with Exchange-Enhancement-for-Large-Gradient (read more) to make TDDFT give accurate Rydberg excitations
  • model-space diabatization for quantum photochemistry (read more)
  • electronic spectrum of thioanisole (read more)
  • nonintuitive nature of diabatic states for thioanisole photochemistry (read more)
  • 42-dimensional potential surfaces and state couplings for thioanisole photodissociation (work in progress)

Congratulations Shaohong!

The accuracy of Kohn-Sham density functional theory depends on the exchange-correlation functional. We have now developed two new functionals, called MN15-L (local) and MN15 (hybrid), that have broader accuracy than any previously available functionals. The properties considered in the parameterization include bond energies, atomization energies, ionization potentials, electron affinities, proton affinities, reaction barrier heights, noncovalent interactions, isomerization energies, atomic excitation energies, absolute atomic energies, and molecular structures. A special consideration is that both new functionals are designed to be accurate for multi-reference systems (MR54 database), single-reference systems (SR313 database), and noncovalent interactions (NC87 database). Both new functionals are available now in Fortran in MFM 2.0, and they will also be included in the next release of Gaussian. Read more: MN15-L and MN15.

MN15

 

April 6, 2016

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