Computational Quantum Chemistry

                 

Principal Investigator

Leo Radom

Research School of Chemistry

 

Chemistry is traditionally an experimental science. However, recent advances in computational techniques and the development of highly efficient computer algorithms allows the computer to provide a powerful complement to experiment in the study of the chemistry of small molecules. Theory may particularly be used to advantage for reactive or unstable species for which appropriate laboratory experiments are difficult to perform, and these are therefore the systems on which we focus attention. The principal properties of molecules which we examine are their structures, i.e. their shape in terms of bond lengths and bond angles, and their stabilities, i.e. an assessment of whether the molecules are likely to be long-lived or whether they are likely to decompose easily. We also calculate spectroscopic properties. These are particularly useful as fingerprints for eventual experimental identification (e.g. in the laboratory or in interstellar space) of molecules which have hitherto not been observed.

   

Co-Investigators

       

Andrew Chalk

Allan East

James Gauld

Hans Heuts

Paul Mayer

Mark McDonald

Athanassios Nicolaides

Danne Rasmussen

Anthony Scott

David Smith

Research School of Chemistry

Brian Smith

Biomolecular Research Institute

Melbourne

Richard Wong

University of Queensland

       
               

     
               

What are the results to date and the future of the work?

During 1996, our computational research focussed on the following principal themes: gas-phase ion chemistry, organic reactive intermediates, radical cation chemistry, theoretical thermochemistry, planar tetracoordinate carbon, nucleophilic substitution reactions, enzyme-mediated reactions, free radical chemistry and polymerization.

We will continue to use theory to examine the properties of reactive species for which appropriate experimental measurements are difficult. We hope that our predictions will continue to stimulate relevant experiments. In the longer term, the computer calculations may prove useful in the design of new materials and pharmaceuticals.

 

Projects

k29, p03,q07, q08, r54

s08, v01, v55, v56 - VPP, PC

 
                 

- Appendix A


 
                 

     

What computational techniques are used?

The ab initio molecular orbital calculations required to provide reliable information on molecular structures and reaction mechanisms are extremely computationally intensive. The program packages that we use include GAUSSIAN 94, ACES II and MOLPRO.

Publications

Cioslowski, J., Scott, A.P., Radom, L., Catastrophes, Bifurcations and Hysteretic Loops in Torsional Potentials of Internal Rotations in Molecules, Molecular Physics, in press.

Curtiss, L.A., Redfern, P.C., Smith, B.J., Radom, L., Gaussian-2 Theory: Reduced Basis Set Requirements, Journal of Chemical Physics, 104, 1996, 5148­5152.

East, A.L.L., Radom, L., A Comparison of High-Quality Ab Initio Basis Sets: The Inversion Barrier in Ammonia, Journal of Molecular Structure, 376, 1996, 437­447.

East, A.L.L., Radom, L., Ab Initio Statistical Thermodynamical Models for the Computation of Third-Law Entropies, Journal of Chemical Physics, in press.

Gauld, J.W., Audier, H., Fossey, J., Radom, L., Water-Catalyzed Interconversion of Conventional and Distonic Radical Cations: Methanol and Methyleneoxonium Radical Cations, Journal of the American Chemical Society, 118, 1996, 6299­6300.

Gauld, J.W., Glukhovtsev, M.N., Radom, L., The Structure of the Methanol Radical Cation: An Artificially Short CO Bond with MP2 Theory, Chemical Physics Letters, 262, 1996, 187­193.

Gauld, J.W., Holmes, J.L., Radom, L., An Evaluation of Additivity Schemes for the Estimation of Heats of Formation of Distonic Radical Cations, Acta Chemica Scandinavica, in press.

Glukhovtsev, M.N., Bach, R., Pross, A., Radom, L., The Performance of B3­LYP Density Functional Theory in Describing SN2 Reactions at Saturated Carbon, Chemical Physics Letters, 260, 1996, 558­564.

Glukhovtsev, M.N., Pross, A., Radom, L., Acidities, Proton Affinities and Other Thermochemical Properties of Hypohalous Acids, HOX (X = F ­ I): A High Level Computational Study, Journal of Physical Chemistry, 100, 1996, 3498­3503.

Glukhovtsev, M.N. Pross, A., Radom, L., Gas-Phase Non-Identity SN2 Reactions of Halide Anions with Methyl Halides: A High Level Computational Study, Journal of the American Chemical Society, 118, 1996, 6273­6284.

Glukhovtsev, M.N., Pross, A., Schlegel, H.B., Bach, R., Radom, L., Gas-Phase Identity SN2 Reactions of Halide Anions and Methyl Halides with Retention of Configuration, Journal of the American Chemical Society, 118, 1996, 11258­11264.

Heuts, J.P.A., Gilbert, R.G., Radom, L., Determination of Arrhenius Parameters for Propagation in Free-Radical Polymerizations: An Assessment of Ab Initio Procedures, Journal of Physical Chemistry, 100, 1996, 18997­19006.

Heuts, J.P.A., Pross, A., Radom, L., Hydrogen Transfer Between Ethyl Radical and Ethylene: An Example Where Kinetics Does Not Follow Thermodynamics, Journal of Physical Chemistry, 100, 1996, 17087­17089.

     

     

     

McKee, M.L., Nicolaides, A., Radom, L., A Theoretical Study of Chlorine Atom and Methyl Radical Addition to Nitrogen Bases: Why Do Cl Atoms Form Two-Center­Three-Electron Bonds Whereas CH3 Radicals Form Two-Center­Two-Electron Bonds? Journal of the American Chemical Society, 118, 1996, 10571­10576

Nicolaides, A., Radom, L., An Evaluation of the Performance of G2, G2(MP2) and G2(MP2,SVP) Theories for Heats of Formation and Heats of Reaction in the Case of "Large" Hydrocarbons, Molecular Physics, 88, 1996, 759­765.

Nicolaides, A., Radom, L., Relative Stabilities and Hydride Affinities of Silatropylium and Silabenzyl Cations and their Isomers. Comparison with the Carbon Analogues Tropylium and Benzyl Cations, Journal of the American Chemical Society, 118, 1996, 10561­10570.

Nicolaides, A., Rauk, A., Glukhovtsev, M.N., Radom, L., Heats of Formation From G2, G2(MP2) and G2(MP2,SVP) Total Energies, Journal of Physical Chemistry, 100, 1996, 17460­17464.

Scott, A.P., Agranat, I., Biedermann, P.U., Riggs, N.V., Radom, L., Fulvalenes, Fulvenes and Related Molecules: An Ab Initio Study, Journal of Organic Chemistry, in press.

Scott, A.P., Radom, L., Harmonic Vibrational Frequencies: An Evaluation of HartreeFock, Møller-Plesset, Quadratic Configuration Interaction, Density Functional Theory and Semiempirical Scale Factors, Journal of Physical Chemistry, 100, 1996, 16502­16513.

Scott, A.P., Radom, L., Ketene and Ketene Radical Cation: The Unusual Effect of Methyl and Dimethyl Substitution, International Journal of Mass Spectrometry and Ion Processes, in press.

     

- Appendix A