Van De Gohm Researches Innovative Field of Computational Chemistry

August 9, 2011 Sarah Schwartz

Chemistry major Chelsey Van de Gohm ’12 is conducting summer research with Dr. Emanuele Curotto, Professor of Chemistry. Exploring a field of theoretical and computational chemistry that is largely in its infancy, Van de Gohm helps to conduct and interpret simulations of several molecular species of ammonia.

Ortho Hydrogen, Para Hydrogen and Hydro Deuteride, three of the molecular species that Curotto and Van de Gohm plan on exploring, are composed of low mass molecules. These prove to be some of the most difficult when attempting to create simulations. Curotto's ongoing research has been responsible for advances in numerical methodologies, which overcome the unique difficulties encountered. Their breakthroughs include the implementation of Stereographic Projection Paths integral for simulations of rotations of rigid bodies, as well as the use of stereographic projection coordinates for the Diffusion Monte Carlo algorithm. These methods have allowed Curotto to perform simulations of systems that would have required too many resources with traditional methods.

"These species of ammonia molecules are treasure troves of information, unusual quantum phenomena, and knowledge that can be critical to many fundamental and applied fields of research," explains Curotto. "Understanding the basic structural and thermodynamic properties of different combination of hydrogen bonded systems mixed with the hydrogen species, could lead to critical insights into the problem of hydrogen storage for the transportation industry."

Curotto recently developed a general procedure based on the distributed multipole expansion approach to construct the interaction between hydrogen and one or more molecules. The resulting analytical functions are particularly amenable to generate a variety of potential energy surfaces for the oH and pH2- molecule and/or ions.

Before any of those goals could be achieved, they needed to identify a plausible molecular cluster as a host. So after searching through a large archive of partially completed potential landscapes, Curotto and Van de Gohm settled on the ammonia dodecamer for which a preliminary exploration may have found the correct global minimum but the important structures seemed to be missing.

Consequently, Van de Gohm is monitoring a numerical minimization of the ammonia dodecamer. In order to find a starting point for her new exploration, she is using a dual strategy composed of the genetic algorithm for combining and preserving certain features from the structures. After a "generation" of such best candidates is produced, each starting point is driven toward the minimum in the closest proximity by an algorithm for the integration of the Langevin equation adapted to work in the curved spaces generated by rigid bodies. Each generation consists of 2,000 structures produced and processed using a 20-node Beowulf cluster accessed remotely from a desktop in the laboratory.

For Van de Gohm, the research she is conducting is different than anything she's ever experienced, taking her out of the traditional chemistry lab and into computer-based simulations.

"It's helpful to get a view of a different type of lab situation because it's all computer-based work," says Van de Gohm. "To prepare, I trained on the computer program for the first month and a half of the summer. As my adviser, Dr. Curotto has always encouraged me to participate in summer research. It's really good to get research experience now as a student because Dr. Curotto is there to help me a lot. I think that it helps you grow significantly with your research skills."

As soon as Curotto and Van de Gohm are confident in their results, they can begin the next phase of this research, which involves extending these exploration techniques to three other systems: the para-hydrogen and the dodecamer, ortho-hydrogen and the dodecamer, and hydrogen deuteride and the ammonia dodecamer. This is likely to take place during Fall 2011.

"One of the very best things that Arcadia offers its students is the opportunity to conduct state-of-the-art research one-on-one with our gifted faculty," said Arcadia's President Carl (Tobey) Oxholm III.

"Here, discovery and innovation are not just read about in books—they are experienced with the hands and a mentor. These experiences prepare our students well for graduate schools and careers and help to ensure that our country will have creative minds eager to take on new challenges. But these experiences also create informed citizens, as our students know firsthand how difficult true scientific inquiry is and are better able to evaluate and participate in public discourse about scientific issues that will have local, national and global significance in the coming decades."

chemistryresearch