[CP2K-user] Benefit of contracted basis?

[Nicholas Winner]

Hello all, a quick question:

When employing an auxiliary basis for a system, we have a choice of many 
such as FITx, cFITx, cpFITx... I understand that the "x" refers to the 
number of Gaussian exponents, and that the prefix indicates whether you are 
using uncontracted, contracted, or contracted with additional polarization 
functions, respectively. What I don't know is why you would choose 
contracted/uncontracted. Both end up having the same number of primitive 
basis functions in your calculation if I understand correctly. So what is 
the use of having one over the other?

Thanks for your help.

-Nick

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