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Cost Comparison

The following is from:
Irikura, K. K.; Frurip, D. J. In "Computational Thermochemistry: Prediction and Estimation of Molecular Thermodynamics" (ACS Symposium Series 677); Irikura, K. K., Frurip, D. J., Eds.; American Chemical Society: Washington, DC, 1998; Chapter 1.

Some Common Methods of Computational Chemistrya

Method Applicability Cost Reliabilityb
TypeSize SoftwareComputerPersonnel AccuracycPrecisiond
Empirical (e.g. Benson Groups) common organic any $ $ A- B+
Molecular Mechanics (e.g. MM3) common organic 100000 atoms $ $$ A- B
semi-empirical MO theory (e.g. MNDO/d) organic, some inorganic 500 atoms $ $ $$ C+ C-
density functional theory (e.g. B3LYP) alle 50 atomsf $$$ $$ $$$ B- C+
CBS-4 (MO theory) alle 20 atomsf $$$ $$$ $$$ B B-
BAC-MP4 (corr. MO theory) organic, some inorganic 20 atomsf $$$ $$$ $$$$ B+ B
PCI-80 (corr. MO theory) alle 20 atomsf $$$ $$$ $$$$ B+ B-
G2 (MO theory) alle 6 heaviesf $$$ $$$$ $$$ A- B
CCSD(T) with basis set extrapolation (MO theory) alle 3 heaviesf $$$ $$$$$$ $$$$ A A-

aThe opinions in this Table are those of the authors and do not necessarily represent those of the authors of the other chapters in this book.
bDFT methods are more robust than MO methods for molecules that contain transition metals, although both are less accurate for transition metals than for organics.
cTypical performance for a large set of moelcules.(i.e. mean error)
dWorst-case performance among a large set of moelcules (i.e. largest error)
eSubject to availability of basis sets.
fLight atoms add less than heavy atoms to the computational expense; "heavy" means lithium or heavier.