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Quantum free energies of the conformers of glycine on an ab initio potential energy surface

Miller, Thomas F., III and Clary, David C. (2004) Quantum free energies of the conformers of glycine on an ab initio potential energy surface. Physical Chemistry Chemical Physics, 6 (10). pp. 2563-2571. ISSN 1463-9076. http://resolver.caltech.edu/CaltechAUTHORS:MILpccp04

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Abstract

The torsional path integral Monte Carlo (TPIMC) technique is used to study the five lowest-energy conformers of glycine. The theoretical method provides an anharmonic and quantum-mechanical description of conformational free energy and is used for the first time with an ab initio potential energy surface. The 3-dimensional torsional potential energy surface of glycine was obtained at the MP2/6-311++G** level of theory and is optimized with respect to the non-torsional degrees of freedom. Calculated conformer populations compare well with those reported in recent matrix-isolation infrared spectroscopy experiments. An additional conformer, not yet observed, is predicted to be heavily populated in the thermal equilibria probed by experiment, and a new explanation for its elusiveness is provided. Quantum effects, such as zero point energy, are found to substantially alter conformer populations, and an algorithm for estimating the role of non-torsional vibrations in the conformational thermodynamics of a molecule is introduced.


Item Type:Article
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http://dx.doi.org/10.1039/b314644hDOIUNSPECIFIED
http://www.rsc.org/publishing/journals/CP/article.asp?doi=b314644hPublisherUNSPECIFIED
Additional Information:This journal is © the Owner Societies 2004. Received 13th November 2003, Accepted 2nd February 2004. First published on the web 4th March 2004. T.F.M. and D.C.C acknowledge fellowships from the National Science Foundation and the Leverhulme Trust, respectively. The work was supported by the Oxford Supercomputing Centre and the Engineering and Physical Sciences Research Council. The authors appreciate the helpful comments of Dr. M. Mella, Dr. P.D. Godfrey, Prof. S.G. Stepanian, and Prof. J.P. Simons and his research group. Supporting information available: Tables listing the calculated harmonic frequencies of the glycine conformers.
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Funding AgencyGrant Number
Engineering and Physical Sciences Research CouncilUNSPECIFIED
Oxford Supercomputing CentreUNSPECIFIED
Subject Keywords:SEEDED SUPERSONIC JETS; MONTE-CARLO METHOD; GASEOUS GLYCINE; LARGE MOLECULES; GAS MATRICES; INITIO; ROTAMERIZATION; RELAXATION; SPECTRUM; CLUSTERS
Record Number:CaltechAUTHORS:MILpccp04
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:MILpccp04
Alternative URL:http://dx.doi.org/10.1039/b314644h
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11067
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:25 Jun 2008
Last Modified:26 Dec 2012 10:08

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