TITLE:

A Good Method to Avoid for Treating Internal Rotation in the Partition Function

DATE:

Friday, Sept. 27th, 2013

TIME:

3:30 PM

LOCATION:

GMCS 214

SPEAKER:

Dr. Andrew Cooksy. San Diego State University.

ABSTRACT:

Our software package FEMvib solves the vibrational Schrodinger equation in up to three dimensions on an arbitrary potential energy surface. This analysis allows us to predict vibrational excitation energies in molecules, starting from now-routine electronic structure calculations, in cases where the potential energy is poorly modeled by common approximations (in particular, where the potential is highly anharmonic and where coupling between degrees of freedom varies strongly with excitation). We recently applied FEMvib to a system with coupled internal rotations (two groups spinning about neighboring single bonds) in a small oxyhydrocarbon. The intention is to test several methods for approximating the contribution to the molecular partition function from these motions. Accurate partition functions are needed to estimate the thermodynamic parameters of molecules in combustion chemistry, and these easily excited internal rotations now account for the dominant error in our ability to predict many of those partition functions. Our results, based on explicit calculations of the partition function from the manifold of quantum states, fall between those from typical approximation methods, but also demonstrate why a fully quantum solution is not feasible in most cases, especially at the temperatures relevant to combustion.

HOST:

Dr. Jose Castillo.

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