Essentials of Computational Chemistry

246 7 INCLUDING ELECTRON CORRELATION IN MO THEORY
Isotope shifts in the frequencies, however, showed very close agreement between theory
and experiment, all data agreeing to within 5% for seven different isotopomers.
The authors did examine whether significant non-dynamical correlation effects complicated
the system, but MCSCF calculations with large active spaces failed to identify any
configurations other than the dominant one that entered with coefficients in excess of 0.09,
suggesting that the use of single-reference methods was well justified. Part of the challenge
for this particular system simply derives from its negative charge, which imposes a greater
demand on basis-set saturation. In any case, this example illustrates how deceptively difficult
it can be to converge solution of the Schrödinger equation even for seemingly simple
chemical systems – a mere four heavy atoms.
Bibliography and Suggested Additional Reading
Bartlett, R. J. 2000. ‘Perspective on “On the Correlation Problem in Atomic and Molecular Systems.
Calculations of Wavefunction Components in Ursell-type Expansion Using Quantum-field Theoretical
Methods”’ Theor. Chem. Acc., 103, 273.
Cioslowski, J., Ed. 2001. Quantum-Mechanical Prediction of Thermochemical Data, Kluwer: Dordrecht.
Cramer, C. J. 1998. ‘Bergman, Aza-Bergman, and Protonated Aza-Bergman Cyclizations and Intermediate
2,5-Arynes: Chemistry and Challenges to Computation’ J. Am. Chem. Soc., 120, 6261.
Cramer, C. J. and Smith, B. A. 1996. ‘Trimethylenemethane. Comparison of Multiconfiguration Selfconsistent
Field and Density Functional Methods for a Non-Kekulé Hydrocarbon’ J. Phys. Chem.
100, 9664.
Curtiss, L. A., Raghavachari, K., Redfern, P. C., Rassolov, V., and Pople, J. A. 1998. ‘Gaussian-3
(G3) Theory for Molecules Containing First and Second-row Atoms’, J. Chem. Phys. 109, 7764.
Feller, D. and Davidson, E. R. 1990. ‘Basis Sets for Ab Initio Molecular Orbital Calculations and
Intermolecular Interactions’ in Reviews in Computational Chemistry, Vol. 1, Lipkowitz, K. B.
Boyd, D. B., Eds., VCH: New York, 1.
Hehre, W. J. 1995. Practical Strategies for Electronic Structure Calculations, Wavefunction: Irvine, CA.
Hehre, W. J., Radom, L., Schleyer, P. v. R., and Pople, J. A. 1986. Ab Initio Molecular Orbital
Theory, Wiley: New York.
Jensen, F. 1999. Introduction to Computational Chemistry, Wiley: Chichester.
Levine, I. N. 2000. Quantum Chemistry, 5th Edn., Prentice Hall: New York.
Lynch, B. J. and Truhlar, D. G. 2003. ‘Robust and Affordable Multicoefficient Methods for Thermochemistry
and Thermochemical Kinetics: The MCCM/3 Suite and SAC/3’, J. Phys. Chem. A,
107, 3898.
Martin, J. M. L. 1998. ‘Calibration of Atomization Energies of Small Polyatomics’ in Computational
Thermochemistry, ACS Symposium Series, Vol. 677, Irikura, K. K. and Frurip, D. J. Eds., American
Chemical Society, Washington, DC, 212.
Petersson, G. A. 1998. ‘Complete Basis-set Thermochemistry and Kinetics’ in Computational Thermochemistry,
ACS Symposium Series, Vol. 677, Irikura, K. K. and Frurip, D. J., Eds., American
Chemical Society, Washington, DC, 237.
Petersson, G. A., Malick, D. K., Wilson, W. G., Ochterski, J. W., Montgomery, J. A., Jr., and Frisch,
M. J. 1998. ‘Calibration and Comparison of the Gaussian-2, Complete Basis Set, and Density Functional
Methods for Computational Thermochemistry’ J. Chem. Phys., 109, 10 570.
Slipchenko, L. V. and Krylov, A. I. 2003. ‘Electronic Structure of the Trimethylenemethane Diradical
in its Ground and Electronically Excited States: Bonding, Equilibrium Geometries, and Vibrational
Frequencies’, J. Chem. Phys., 118, 6874.