Basis sets energy-optimized

One disadvantage of all energy optimized basis sets is the fact that they primarily depend on the wave function in the region of the inner shell electrons. The 1 s-electrons account for a large part of the total energy, and minimizing the energy will tend to make the basis set optimum for the core electrons, and less than optimum for the valence electrons. However, chemistry is mainly dependent on the valence electrons ... 

Furthermore, many properties (for example polarizability) depend mainly on the wave function tail (far from the nucleus), which energetically is unimportant. An energy optimized basis set which gives a good description of the outer part of the wave function... 

Therefore this interaction involves only the small component densities of the wavefunction, and can be expected to be very sensitive to these densities. Another example is the possible electric dipole moment of a nucleon. Quiney et al. [21] have shown that the calculation of this interaction depends crucially on the ratio between the large and small component in the nuclear region. For the case of TIF, even large energy-optimized basis sets proved to be unsuitable and had to be replaced by large even-tempered... 

Standard energy-optimized basis sets are not suitable for accurate calculations of electric polarizabilities. The simplest solution - adding the necessary polarization and diffuse functions - makes the basis sets too large to enable efficient calculations for large molecules. Significantly smaller basis sets, designed considering the electric-field dependence of the orbitals (Benkova et al. 2005 Sadie) 1988), provide results of similar or better quality at lower computational cost. 

In general, two modifications of the standard energy-optimized basis sets are needed the standard functions should be uncontracted and tight s, p, and d functions should be added. The s-type functions are of particular importance for the Fermi contact contribution, whereas... 

Huzinaga determined uncontracted energy optimized basis sets up to (10s6p) for first row elements. This was later extended to (14s9p) by van Duijneveldt " and up to (18s,... 

Of cmcial importance in designing a basis set is the issue of linear dependence, because this affects the numerical stability of the atomic or molecular calculations that use the basis sets. Linear dependence in the primitive set can be controlled by the use of even-tempered or well-tempered basis sets, which minimize the linear dependence by construction. However, such basis sets tend to be larger than energy-optimized basis sets, where linear dependence problems can become significant as the basis set size increases. 

---