The G2 Molecule Set and Pitfalls in Its Interpretation

The original paper defining the Gaussian-2 method by Curtiss, Raghavachari, Trucks and Pople tested the method s effectiveness by comparing its results to experimental thermochemical data for a set of 125 calculations 55 atomization energies, 38 ionization potentials, 25 electron affinities and 7 proton affinities. All compounds included only first and second-row heavy atoms. The specific calculations chosen were selected because of the availability of high accuracy experimental values for these thermochemical quantities. 

This molecule set has several strengths which make it valuable for evaluating the accuracy of a model chemistry  

Thermochemical quantities are difficult to model very accurately (so good results really do imply a good method). Errors can generally be assumed to represent a worst-case scenario for the model, and actual results for easier properties may be better. 

The experimental results are well-accepted values with small errors. 

It includes compounds containing a range of different elements. 

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