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When using the EMSL BSE Database and selecting a basis set, one can choose the "Optimized General Contractions" or not. When doing so for, e.g., Nitrogen and the cc-pVDZ some basis functions are not included anymore while the others are kept.

Without "Optimized General Contractions":

N     0 
S   9   1.00
   9046.0000000              0.0007000        
   1357.0000000              0.0053890        
    309.3000000              0.0274060        
     87.7300000              0.1032070        
     28.5600000              0.2787230        
     10.2100000              0.4485400        
      3.8380000              0.2782380        
      0.7466000              0.0154400        
      0.2248000             -0.0028640        <=====
S   9   1.00
   9046.0000000             -0.0001530        
   1357.0000000             -0.0012080        
    309.3000000             -0.0059920        
     87.7300000             -0.0245440        
     28.5600000             -0.0674590        
     10.2100000             -0.1580780        
      3.8380000             -0.1218310        
      0.7466000              0.5490030        
      0.2248000              0.5788150        <=====
S   1   1.00
      0.2248000              1.0000000        
P   4   1.00
     13.5500000              0.0399190        
      2.9170000              0.2171690        
      0.7973000              0.5103190        
      0.2185000              0.4622140        <=====
P   1   1.00
      0.2185000              1.0000000        
D   1   1.00
      0.8170000              1.0000000

With "Optimized General Contractions":

N     0 
S   8   1.00
   9046.0000000              0.0007000        
   1357.0000000              0.0053890        
    309.3000000              0.0274060        
     87.7300000              0.1032070        
     28.5600000              0.2787230        
     10.2100000              0.4485400        
      3.8380000              0.2782380        
      0.7466000              0.0154400        
S   8   1.00
   9046.0000000             -0.0001530        
   1357.0000000             -0.0012080        
    309.3000000             -0.0059920        
     87.7300000             -0.0245440        
     28.5600000             -0.0674590        
     10.2100000             -0.1580780        
      3.8380000             -0.1218310        
      0.7466000              0.5490030        
S   1   1.00
      0.2248000              1.0000000        
P   3   1.00
     13.5500000              0.0399190        
      2.9170000              0.2171690        
      0.7973000              0.5103190        
P   1   1.00
      0.2185000              1.0000000        
D   1   1.00
      0.8170000              1.0000000

What makes the basis set optimized if those three functions are simply omitted?

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  • $\begingroup$ In any case, the option "optimized general contractions" appears to have been removed from the new beta site - at least I couldn't find it... $\endgroup$
    – Buck Thorn
    Mar 20 '19 at 11:51
  • $\begingroup$ There it is in the advanced section. $\endgroup$ Mar 20 '19 at 11:51
  • $\begingroup$ I tried generating the basis from the beta site and got same sets with/wo optimized general flag. Tried it a few times just to convince myself. The older website's output may be a bug? $\endgroup$
    – Buck Thorn
    Mar 20 '19 at 12:03
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Those basis functions are removed because they are considered redundant. There is a completely uncontracted shell with the same exponent and angular momentum, so they can be removed without much loss of accuracy.

N     0 
S   9   1.00
   9046.0000000              0.0007000        
   1357.0000000              0.0053890        
    309.3000000              0.0274060        
     87.7300000              0.1032070        
     28.5600000              0.2787230        
     10.2100000              0.4485400        
      3.8380000              0.2782380        
      0.7466000              0.0154400        
      0.2248000             -0.0028640        <=====
S   9   1.00
   9046.0000000             -0.0001530        
   1357.0000000             -0.0012080        
    309.3000000             -0.0059920        
     87.7300000             -0.0245440        
     28.5600000             -0.0674590        
     10.2100000             -0.1580780        
      3.8380000             -0.1218310        
      0.7466000              0.5490030        
      0.2248000              0.5788150        <=====
S   1   1.00
      0.2248000              1.0000000        ***Same exponent

Unfortunately, this is not documented on the old BSE. Here is the reference:

T. Hashimoto, K. Hirao, H. Tatewaki
'Comment on Dunning's correlation-consistent basis set'
Chemical Physics Letters v243, Issues 1-2, pp, 190-192 (1995)
https://doi.org/10.1016/0009-2614(95)00807-G

There was a period of time when the option was not working on the new BSE website (https://www.basissetexchange.org) but has been fixed (I hope).

Note: I am the maintainer of the new Basis Set Exchange :)

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