The other basis set order is that Minimal < Split Valence < Polarized < Diffuse according to an appropriate approximation to the actual wave function. The number of primitives used affects the accuracy of energy calculation . The energy decreases by increasing the number of primitives benefitting from the calculation. The other issue about the basis set is the polarization basis function, based on the interaction of the neighbouring nuclei. The interaction can distort orbitals; therefore, flexible shapes must be calculated correctly. Polarisation functions have to be added into a basis set to increase accuracy. The other function to augment accuracy is a diffuse function, used to clarify anions, excited states and very electronegative atoms such as fluorine and is significant to describe polarizabilities or binding energies of van der Waals accurately. An example of combining these functions to a basis set is aug-cc-pVXZ. For instance, 'cc' means "correlation consistent", 'p' means "polarisation functions added", and 'aug' means "augmented" with (essentially) diffuse functions .