An effective scheme for selecting basis sets for ab initio calculations

An effective scheme for selecting economical basis sets for ab initio calculations has been proposed for wide-range systems based on the analysis of different functions in the currently used basis sets. Accordingly the selection of the basis sets should be made according to the different properties and real chemical surrounding of the atoms in the systems. For normal systems, the size and level of the basis sets used for the descriptions of the constituent atoms should be increased from left to right according to the position of the atom in the periodic table. Moreover, the more the atom is negatively charged, the more the basis functions and suitable polarization functions and diffuse functions should be utilized. Whereas, for the positively charged atoms, the size of basis set may be reduced. It is not necessary to use the polarization and diffuse functions for the covalently saturated atoms with normal valence states. However, for the system involving hydrogen-bonding, weak interactions, functional groups, metallic bonding with zero valence or low positive valence, and other sensitive interactions, the polarization and diffuse functions must be used. With this scheme, reliable calculation results may be obtained with suitable basis sets and smaller computational capability. By detailed analysis of a series of systems, it has been demonstrated that this scheme is very practical and effective. This scheme may be used in Hartree-Fock, Moller-Plesset and density functional theoretical calculations. It is expected that the scheme would find important applications in the extensive calculations of large systems in chemistry, materials science, and life and biological sciences.