Question

There is 6-31G(d) in Chemistry basis set.
What does 6,3,1,G,d mean for each?

Answer 1

6-31G(d) = basis set

Basis set is set of function to create the molecular orbitalsand which are expanded as a linear combination with the coefficients.

where,

6 = Is the number of gaussian function summed to describe the inner shell orbital.

3 = It is the function for valence orbital

also it is the number of gaussian function that comprise the first STO of the double zeta.

1 = It is the function for valence orbital

also it is the number of gaussian function that summed in the second STO

d = It is the function for atoms other than hydrogen.

G = Gaussian function

where STO is a function used in atomic orbital in the linear combination.