Basis set selection

Part 2, Model Chemistries, begins with Chapter 5, Basis Set Effects. This chapter discusses the most important standard basis sets and presents principles for basis set selection. It also describes the distinction between open shell and closed shell calculations. 

The Bethe Sum Rule and Basis Set Selection in the Calculation of Generalized Oscillator Strengths... 

Mosley R.T., Culberson J.C., Kraker B., Feuston B.P., Sheridan R.P., Conway J.F., Forbes J.K., Chakravorty S.J., Kearsley S.K., Reagent selector using synthon analysis to visualize reagent properties and assist in basis set selection. J. Chem. Inf. Model. 2005, 45, 1439-1446. 

We have recently completed a detailed study (27) of the dipole moment, electron affinity, and polarizability of LIF and the Isoelectronic BeO molecule. A wide range of basis sets were investigated to assure convergence of each of the properties and to serve as a guide for basis set selection for the heavier alkali halides. The results at the equilibrium geometries of LIF and BeO are compared in Table 1 together with those for HF, for which experimental polarizabilities are known. The columns... 

The general rules noted above make of course not the problem of the basis set selection solved. In some cases the use of basis sets of nonstandard composition is required. We comment on some of them. First,... 

For the sake of compactness, we embodied the knowledge about the basis set selection in Table 2,18. This Table provides of course only... 

Technical aspects of supermolecule calculation need not be noted specifically since they are essentially the stitne as those mentioned in the previous section. Hints for the basis set selection given in Table 5,16 may be supplemented with a note referring to proton potential curves. Small basis sets give potential curves with a single minimum... 

Table 3 Effect of Basis Set Selection on Bond Angle and Bond Length...

Perhaps more challenging to resolve than the choice of electron correlation treatment for weak interaction problems is the basis-set selection. Partly, this reflects the fact that basis sets have traditionally been devised for describing chemical bonding, not for the subtle juxtaposition of effects in weak interaction. They have to do both for weak interaction potential evaluations. This issue in basis-set selection, the adequacy of the basis to describe the electronic structure effects that comprise the interaction, can impose more stringent requirements than for describing an isolated molecule. Consider polarization as a contributor to interaction. Since the adequate determination of molecular polarizabilities requires basis sets augmented with diffuse and higher-/ basis functions [37], an... 

A study has been made of the effect of basis set selection on ab-initio SCF calculations of molecular hardness.Not surprisingly, the value of the LUMO energy, which is set equal to — A, is the term which changes most. This means that the hardness calculated from Equation (4.22) will be very sensitive to the quality of the calculations. Of course, /z will also vary greatly. But as long as the same basis set, or its equivalent, is used to compare different structures, or similar molecules, relative values of rj and /z are found which are usually reliable. 

In summary, it seems to me that the ab initio techniques are far from having been fully exploited. There is no doubt that these high-order properties will not only be sensitive to basis-set selection and electron correlation, as we would expect, but also to the coupling of electron correlation with dispersion. 

The CBS family employs the asymptotic convergence of pair natural orbital expansions to extrapolate to the MP2 limit and the higher order contributions for the various components of the electronic energy are evaluated with a smaller basis set selected to balance the errors and CPU times [224],... 

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