THEORETICAL & COMPUTATIONAL CHEMISTRY RESEARCH
Computational Methods
Computational chemists' daily work influences our understanding of the way the world works, helps manufacturers design more productive and efficient processes, characterizes new compounds and materials, and helps other researchers extract useful knowledge from mountains of data. Computational chemistry is also used to study the fundamental properties of atoms, molecules, and chemical reactions, using quantum mechanics and thermodynamics. (www.acs.org)
Many computational chemists use theoretical models and computer-based simulations to:
Make predictions for experiments that are too difficult, expensive, or time-consuming; or
Give a more thorough understanding of the underlying chemistry from experimental chemistry observations.
However, these theoretical models are not perfect. Oftentimes, we have to compromise between how accurate we can make a calculation versus how big a molecule we can simulate.
If you're a student and interested in computational chemistry research, please contact Dr. Chulhai at chulhaid@uindy.edu.
Plasmonic Nanoparticles
Nanoparticles are particles that are a few nanometers in size. However, their size and shape gives them chemical and physical properties that are very different from their bulk counterpart.
For example, gold is, well, gold colored in bulk materials. However, nanoparticle gold can absorb and reflect almost any color — depending on it’s size and shape.
Nanoparticles have been used for centuries, long before anyone knew what they were. The beautiful colors in most stained glass are because of nanoparticles.
To understand how nanoparticles interact with light, we make atomistic models of nanoparticles of various sizes and shapes, and simulate their properties using electrodynamics.
Just some of the uses of nanoparticles include:
Treatments of certain types of cancer;
Making efficient solar cells;
Create biodegradable materials;
Help clean up pollution;
Creating smaller, more efficient transistors;
Create new and more efficient catalysts.
Enhanced Spectroscopy
Spectroscopy is the study of how light interacts with matter. We often use spectroscopy to identify unknown molecules. But what happens when the number of molecules present are too low to detect?
It turns out that nanoparticles can also enhanced the spectra of molecules attached to their surface such that we can see the spectrum from a single molecule! This introduced a whole new field of chemistry called surface-enhanced spectroscopy.
However, the enhanced spectrum now changes depending on things like how the molecule binds to the surface. We can therefore use computation to figure out exactly how molecules bind to the surface of nanoparticles. We have even been able to see how a single molecule vibrates on the surface of a nanoparticles!
Surface enhanced spectroscopy allows us to look at the world with unprecedented levels of detail. We are just beginning to understand all of the exciting new chemistry we can do with these techniques.
Quantum Embedding
Sometimes we want high accuracy calculations for large molecules. How do we go about doing that?
In a lot of chemical systems, the interesting chemistry happen in only a small region of the overall molecule, for example, in active sites of proteins. In these cases, we use quantum embedding methods, which use a high accuracy method for the small, important region, and a low accuracy method for the remainder of the system.
We use a projection-based quantum embedding method that enforces the Pauli Exclusion Principle by shifting occupied orbital energies (see above). Doing so allow us to get very high accuracy results for very low computational cost in these large chemical systems. Some of these examples are shown below.
We can use projection-based embedding to break a molecule up into as many pieces as we want to. The results above are for a benzene molecule accurately broken up into atomic pieces.
We can now study reactions, where only a small part (ball model above) is described using a very high level of theory.