Research

I often describe our research as ‘chemistry without chemicals‘ because our work utilizes physics, mathematics and high performance computing to gain insight into important chemical problems instead of performing experiments in a lab. We compute/model/simulate the structures, energetics and other properties of atomic and molecular systems as well as chemical processes by using computers to numerically solve the quantum mechanical electronic Schrödinger equation.

A great deal of chemistry is governed by the behavior of electrons in atoms and molecules (bonding, oxidation, reduction, excited states, etc.). Electrons are so small that quantum mechanics, rather than classical mechanics, is required to correctly describe their physics. Consequently, sufficiently accurate solutions to the electronic Schrödinger equation can provide insight into and predictions about a wide range of chemical phenomena, in much the same way that solutions to Newton’s equations of motion can provide information about the trajectory of a projectile. Due to the complexity of the underlying mathematics, such solutions to the Schrödinger equation can often only be obtained with substantial computational resources.

Ab initio Studies of Weak Non-Covalent Interactions

Weak non-covalent interactions within and between molecules play vital roles in a host of chemical, physical and biological processes (e.g., hydrogen bonding, London dispersion forces, halogen bonding, di-hydrogen bonding, π-type stacking interactions, etc.). Using accurate quantum mechanical electronic structure techniques, we probe the details of the underlying physics behind these interactions. We are also developing new computational methods that can reliably describe weak chemical interactions in larger chemical or biochemical systems.

Development of New Theoretical Methods for Non-Covalent Clusters

Doing more with less: We are developing new computational strategies to make the characterization of structural, energetic and spectroscopic properties with high-accuracy quantum mechanical (QM) methods not only possible for sizable non-covalent clusters but also practical with modest computational resources. With our multi-centered extension of Morokuma’s ONIOM technique, it is possible to recast the traditional many-body expansion of the interaction energy into the ONIOM formalism. For example, our N-body:Many-body procedure is effectively a 2-layer QM:QM technique that applies a high-level QM method such as CCSD(T) to the leading N terms of the expansion while the trailing terms are recovered with a less demanding low-level method. The ONIOM-like expression of the many-body expansion greatly facilitates the derivation and implementation of analytic gradients for geometry optimizations and Hessians for vibrational frequencies as well as other properties associated with linear operators.

Select Applications and Collaborations

Quantum chemistry can be a powerful tool for both guiding and understanding experiments. Consequently, research projects in my group span a very diverse range of topics. We not only study the fundamentals of non-covalent interactions but also collaborate with experimental groups working in physical, organic, inorganic, bio, (nano)materials and other areas chemistry.

  • Interrogation of non-covalent interactions in the condensed phase with vibrational spectroscopy (e.g., Raman and IR)
  • Computationally informed design of organic chromophores for use in dye sensitized solar cells (DSCs) and biological imaging
  • Characterization of halogen bonding interactions in building blocks for optoelectronic devices (e.g., organic light emitting diodes, OLEDs, and organic photovoltaics, OPVs)
  • Structures and energetics of water clusters and other homogeneous molecular aggregates held together by hydrogen bonds (e.g., (H2O)n, (HF)n (HCl)n)
  • Acid dissociation in micro-hydrated environments (HF, HCl, H2SO4, etc.)
  • Rigorous comparison to available experimental vibrational frequencies and dissociation energies for small homo- and heterogeneous hydrogen bonded clusters (dimers, trimers, etc.) composed of H2O, HF, HCl, HCN, H2S, etc.
  • Hydration and cluster formation of atmospheric species (N2, O2, CO2, Cl, etc.)
  • Solvent stabilized radical anions whose parent neutral molecules have negative electron affinities
  • π-type stacking interactions in proteins
  • Spectroscopic characterization of high energy density materials (explosives, propellants, etc.) and their decomposition products
  • Intramolecular hydrogen bonding