Computational Chemistry Comparison and Benchmark Database
R.D. Johnson III
Objective: (1) To provide a benchmark set of molecules and reactions for the evaluation of ab initio computational methods. (2) To allow the comparison between different ab initio computational methods and experiment for the prediction of thermochemical properties. This will allow accuracy in the computed thermochemical properties to be estimated.
Problem: As computer power increases, there is more reliance on modeling and computational chemistry in the chemical industry. This use is owed to the increased safety and speed, and decreased cost of models and calculations when compared with laboratory measurements. This trend will continue as the computers and software become more powerful. Ab initio computational chemistry methods can provide accurate values for structures, entropies, and heats of formation. However, the cost of the calculation increases greatly as the accuracy increases. The errors in the computational methods are systematic, depending on the method and functional groups that compose the molecule. In order to take advantage of the computational methods, accuracy and cost need to be evaluated. A set of test molecules is needed for this evaluation. There are small sets of species for comparing theory and experiment [L. A. Curtiss et al., J. Chem. Phys. 109, 42 (1998)], but a recent workshop on Computational Thermochemistry at the ACS 212th National Meeting identified the need for a larger set of species, on the order of 500.
Approach: In order to facilitate testing, we selected a set of benchmark molecules and reactions with reliable thermochemical and spectral data and for which both the values and the uncertainties had been evaluated. These measured data include gas-phase enthalpies of formation, entropies, vibrational frequencies, and structures. In addition, we are generating data from ab initio calculations for comparison with experiment. The calculations cover eighteen methods using six basis sets.
The presentation will be through a Web interface where a user can select a subset of molecules from the database (e.g., all species containing phosphorus or an NH2 group), and the property for comparison (e.g., heat of formation). The user will be presented the experimental and calculated values as a table or chart. By comparing the experimental and computed thermochemical values for a given set of molecules, the systematic errors in the computed values can be determined.
Results and Plans: A set of over 600 species with well-known enthalpies of formation has been assembled. Both experimental and calculated values are accessible over the web. Tools are being developed for viewing and accessing this data, such as comparing experimental or theoretical enthalpies of atomization at a given temperature, and comparing reaction energies for user-specified reactions. Experimental data are being collected and evaluated. Ab initio calculations are ongoing. In addition to heats of formation, structures and vibrational energy levels are being included. Beta testers are reviewing the database now. (Web site: http://srdata.nist.gov/cccbdb/).
[Table of Contents | Previous Highlight | Next Highlight]
Last modified: 21 February 2000