Primitive basis set

In molecular quantum dynamics, the choice of the set of coordinates to describe the physical system and to express the Hamiltonian operator is very important. As explained above, the main problem we have to face is the very large size of the basis sets, primitive or contracted, and this size is directly linked to the correlation between the coordinates. An inadequate set of coordinates can entail a strong artificial correlation and thus a poor convergence. Consequently, the set of coordinates must be carefully chosen to minimize as much as possible the size of the basis set. First, it is important to spUt the set of coordinates into two subsets. 

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