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John Herbert

Associate Professor
Physical, Theoretical, Chemical Physics
2114 Newman & Wolfrom Laboratory
614-292-6851
herbert@chemistry.ohio-state.edu

John Herbert received B.S. degrees in chemistry and mathematics from Kansas State University in 1998, where he was a Barry M. Goldwater Scholar. He received a Ph.D. in physical chemistry from the University of Wisconsin-Madison in 2003, where he was a National Defense Science and Engineering Graduate Fellow with John Harriman. This was followed by postdoctoral work with Anne McCoy at The Ohio State University and, subsequently, with Martin Head-Gordon at the University of California-Berkeley, where he was a National Science Foundation Mathematical Sciences Postdoctoral Fellow. He joined the Ohio State faculty in 2006. In 2008, Professor Herbert received a CAREER award from the National Science Foundation; in 2009 he received a Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House Office of Science and Technology Policy; in 2010 he received an Alfred P. Sloan Foundation Research Fellowship, and an ACS Outstanding Junior Faculty Award in Computational Chemistry. In 2011 he was promoted to associate professor.

Electronic structure theory and molecular quantum mechanics

Our group is pursuing a detailed understanding of spectroscopy and chemical dynamics in complex systems, especially macromolecules and condensed phases.  A major goal is to extend ab initio quantum chemistry, with its impressive track record of providing detailed and predictive explanations for molecular phenomena, into condensed-phase environments, where most chemistry actually happens.  This work proceeds on two fronts:

  • Reducing the cost of ab initio electronic structure models and algorithms, which generally increases steeply as a function of the number of atoms in the system.  This can be accomplished either by developing more efficient numerical algorithms, or by developing better theories or models that are intrinsically lower-scaling.  Any reduction in cost makes quantum chemistry amenable to larger systems or longer simulation time scales. 
  •  Improving the accuracy of force-field ("molecular mechanics") and continuum models that can be coupled to electronic structure theory, in order to describe the condensed-phase environment of a quantum-mechanical system in a cost-effective manner.

Recent (and ongoing) projects in the group include:

 

Excited electronic states in macromolecules

The excited electronic states of many small chromophores are well-characterized in the gas phase, but much less is known regarding how these states are perturbed by a solvent, or by some other condensed-phase environment such as the interior of a protein. The location of conical intersections, as well as energy barriers along an excited-state reaction pathway, may be profoundly different in the condensed phase than they are in the gas phase, and these details ultimately dictate whether the energy deposited into a chromophore by a visible or UV photon manifests as fluorescence, radiationless decay to the ground state (internal conversion), or else initiates some excited-state (photochemical) reaction.

The photochemistry and photophysics of DNA are especially interesting topics, due to this molecule's large size, dense manifold of electronic states, and wide variety of electronic interactions. These features present formidable challenges for contemporary electronic structure methods, and we are developing new methods to address these challenges. Improvements to time-dependent density functional theory, QM/MM models, and continuum solvation models have all been necessary in order to make progress in understanding the ground- and excited-state electronic structure of DNA.

Electronic structure in liquid solution

Most chemical reactions happen in the liquid phase, and a detailed theoretical description of chemical reactivity should therefore combine quantum mechanics (which can describe bond-breaking) with statistical mechanics (to include averaging over solvent configurations). However, low-cost electronic structure methods such as density functional theory are often deficient in their ability to describe radicals and certain types of intermolecular interactions, that is, they are often inadequate for precisely the types of chemical species and interactions that are needed to describe a condensed-phase chemical reaction.

To address this challenge, we are developing new, low-cost electronic structure models that can be used to calculate wavefunctions in liquid solution, so that we do not need to rely on density functional theory. These methods take advantage of natural disparities in the length scales of various types of interactions, in order to provide a relatively low-cost solution to Schrödinger's equation, even in a high-dimensional liquid environment. The ultimate goal is to perform efficient, all-electron, and parameter-free simulations of condensed-phase chemical reactions.

More information on these and other projects can be found on Prof. Herbert's research group web page.

A complete publication list is available from Professor Herbert's research web page. Some representative publications from the last few years are listed here.

  1. A simple polarizable continuum model for electrolyte solutions. A.W. Lange and J.M. Herbert, J. Chem. Phys. 134 204110 (2011).
  2. An efficient, fragment-based electronic structure method for molecular systems: Self-consistent polarization with perturbative two-body exchange and dispersion. L.D. Jacobson and J.M. Herbert, J. Chem. Phys. 134 094118 (2011).
  3. Nature's most squishy ion: The important role of solvent polarization in the description of the hydrated electron. J.M. Herbert and L.D. Jacobson, Int. Rev. Phys. Chem. 30, 1 (2011).
  4. Polarizable continuum reaction-field solvation models affording smooth potential energy surfaces. A.W. Lange and J.M. Herbert, J. Phys. Chem. Lett. 1, 556 (2010).
  5. Polarization-bound quasi-continuum states are responsible for the "blue tail" in the optical absorption spectrum of the aqueous electron. L.D. Jacobson and J.M. Herbert, J. Am. Chem. Soc. 132, 10000 (2010).
  6. A one-electron model for the aqueous electron that includes many-body electron-water polarization: Bulk equilibrium structure, vertical electron binding energy, and optical absorption spectrum. L.D. Jacobson and J.M. Herbert, J. Chem. Phys. 133, 154506 (2010).
  7. Both intra- and interstrand charge-transfer excited states in aqueous B-DNA are present at energies comparable to, or just above, the 1ππ* excitonic bright states. A.W. Lange and J.M. Herbert, J. Am. Chem. Soc. 131, 124115 (2009).
  8. A long-range-corrected density functional that performs well for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states. M.A. Rohrdanz, K.M. Martins, and J.M. Herbert, J. Chem. Phys. 130, 054112 (2009).
  9. Charge-transfer excited states in a π-stacked adenine dimer, as predicted using long-range-corrected time-dependent density functional theory. A.W. Lange, M.A. Rohrdanz, and J.M. Herbert, J. Phys. Chem. B 112, 6304 (2008).
  10. Charge penetration and the origin of large O–H vibrational red shifts in hydrated-electron clusters, (H2O)n–. J.M. Herbert and M. Head-Gordon, J. Am. Chem. Soc. 128, 13932 (2006).
  11. Curvy-steps approach to constraint-free, extended-Lagrangian molecular dynamics, using atom- centered basis functions: Convergence toward Born-Oppenheimer trajectories. J.M. Herbert and M. Head-Gordon, J. Chem. Phys. 121, 11542 (2004).