Computational Chemistry Comparison and Benchmark

R.D. Johnson III, NIST Computational Chemistry Comparison and Benchmark Database, NIST Standard Reference Database Number 101, Release 12,2005. Available at http //srdata.nist.gov/ cccbdb... 

The choice of fundamental approximation, combined with the choice of parameter values, defines a particular SEMOT method, analogous to a force field in MM. Several established and novel SEMOT methods have been reviewed and compared elsewhere [54]. Among the three popular SEMOT methods mentioned earlier, MNDO/d is least widely available in commercial software packages. The other two methods, AMI and PM3, differ only in their parameterization. Since the PM3 method was parameterized more recently and more carefully, it is expected to be more reliable and will be the focus of discussion here. However, performance varies, so it should be compared with that of the experiment for related systems before putting faith in the predictions. Note that AMI and PM3 predictions are included in the Computational Chemistry Comparison and Benchmark Database (CCCBDB), which is a convenient, on-line resource for comparing theoretical predictions with experimental data [55]. 

Jonhson RD III (ed) (2006) Computational chemistry comparison and benchmark database. NIST Standard reference database vol 101. http //www.srdata.nist.gov/cccbdb... 

CCCBDB NIST Computational Chemistry Comparison and Benchmark Database... 

In the next two subsections, we describe collections of calculations that have been used to probe the physical accuracy of plane-wave DFT calculations. An important feature of plane-wave calculations is that they can be applied to bulk materials and other situations where the localized basis set approaches of molecular quantum chemistry are computationally impractical. To develop benchmarks for the performance of plane-wave methods for these properties, they must be compared with accurate experimental data. One of the reasons that benchmarking efforts for molecular quantum chemistry have been so successful is that very large collections of high-precision experimental data are available for small molecules. Data sets of similar size are not always available for the properties of interest in plane-wave DFT calculations, and this has limited the number of studies that have been performed with the aim of comparing predictions from plane-wave DFT with quantitative experimental information from a large number of materials. There are, of course, many hundreds of comparisons that have been made with individual experimental measurements. If you follow our advice and become familiar with the state-of-the-art literature in your particular area of interest, you will find examples of this kind. Below, we collect a number of examples where efforts have been made to compare the accuracy of plane-wave DFT calculations against systematic collections of experimental data. 

Regarding TDDFT benchmark studies of chiroptical properties prior to 2005, the reader is referred to some of the initial reports of TDDFT implementations and early benchmark studies for OR [15,42,47,53,98-100], ECD [92,101-103], ROA [81-84], and (where applicable) older work mainly employing Hartree-Fock theory [52,55, 85,104-111], Often, implementations of a new quantum chemistry method are verified by comparing computations to experimental data for relatively small molecules, and papers reporting new implementations typically also feature comparisons between different functionals and basis sets. The papers on TDDFT methods for chiroptical properties cited above are no exception in this regard. In the following, we discuss some of the more recent benchmark studies. One of the central themes will be the performance of TDDFT computations when compared to wavefunction based correlated ab initio methods. Various acronyms will be used throughout this section and the remainder of this chapter. Some of the most frequently used acronyms are collected in Table 1. 

Other publications, however, report more accurate values of B3LYP gas phase Gibbs free energy calculations on aliphatic amines, diamines, and aminoamines. In 2007 Bryantsev et al. reported that B3LYP calculations with the basis set 6-31-h-G had a mean absolute error of 0.78 kcal/mol from experimental values of the gas phase basicity (AGg s) of the reverse reaction of equation 1 reported in the NIST database [58]. This accuracy is comparable to that of expensive, high level model chemistries, but because the experimental values have uncertainties of 2 kcal/mol, it is difficult to discern exactly how accurate the calculations are in comparison to values in the other publications [81]. The take-home message remains the same always benchmark DFT calculations for the systems you are interested in computing [52]. 

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