# Quantum Chemistry

# Theoretical and Computational Chemistry

Quantum chemistry is a branch of chemistry that employs the principles of quantum mechanics** **to address a number of aspects and phenomena associated with chemical systems and reactions from a theoretical point of view. Theoretical quantum chemistry, also often referred to as computational chemistry, makes use of computer algorithms to solve the Schrödinger equation of a given chemical system to predict it's structure, behavior, or properties.

**Solving the Schrödinger Equation**

The Schrödinger equation is the mathematical equation that describes the evolution of a system in time. It should be able to describe the whole world, from the hydrogen atom to the universe! The solution of the equation are energy levels, or orbitals, depicting the quantized atomic picture that chemists use. From those energies, a number of properties such as the electronic structure, thermodynamic quantities, rate constants, and spectroscopic data can be determined. However, the Schrödinger equation can only be exactly solved for the Hydrogen atom, and researchers have devised a number of approximations that range in sophistication. Based on those various approaches, simulations and calculations can be performed on a wide variety of systems ranging from small exotic systems composed of a handful of atoms to entire proteins and their immediate environment.

# At the Pittsburgh Quantum Institute

Theoretical chemistry is thus a powerful tool that allow to either explain experimental measurements or to predict behaviors that have yet to be observed. Researchers at the Pittsburgh Quantum Institute use and refine these tools and apply them to the study of a variety of phenomena and systems. Methodological development is an important research thrust at PQI; for instance, stochastic approaches such as the diffusion Monte Carlo method and Energy Decomposition Analysis are developed at PQI.

Dynamics simulations are used to model the evolution of the system in time, with applications in biochemistry or biophysics, where transport of ions in biological channels or protein folding and binding can be investigated. Computational drug design is also one of the most representative application of computational chemistry, as thousands of compounds can be easily and quickly screened for compatibility in terms of structure and energetics. Similarly, the vast configuration space of materials structure and properties can be explored through simulations towards the building of functional devices from the bottom up, the design of electrolytes for next generation batteries, the identification of biomaterials for energy storage and separation applications, or the characterization of optimal structures for organic and hybrid solar cells.

**Experimental Quantum Chemistry**

PQI researchers study the fundamental chemical forces controlling the composition, atomic structure, and optoelectronic properties of nanoparticles for environmental remediation and catalysis applications. Another research thrust is the use of various analytical methods to investigate the mechanism for enantioselectivity between chiral samples such as thin films and peptides. Similarly, the capabilities of the ion-trap mass spectrometer are used to elucidate the structure, determine the relative stability, and probe the general patterns in chemical reactivity of gas-phase metal ion complexes.

**Related Members**

- Lillian Chong
- Rob Coalson
- Jeffrey Evanseck
- Geoff Hutchison
- Karl Johnson
- Ken Jordan
- John Keith
- Hyung Kim
- Daniel Lambrecht
- Peng Liu
- Noa Marom
- Jill Millstone
- Giannis Mpourmpakis
- Michael van Stipdonk
- Venkat Viswanathan
- David Waldeck
- Judy Yang