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Difference in the Basis Set: Si case

The following example of basis set input are followed by the printed output.

 Si, Pople STO-3G minimal basis set. The value of the scale factor "0." means standard Pople scale factor.

14 3
1 0 3  2.  0.
1 1 3  8.  0.
1 1 3  4.  0.

*******************************************************************************
   ATOM  X(AU)  Y(AU)  Z(AU)    NO. TYPE  EXPONENT    S COEF     P COEF   D/F/G 
 *******************************************************************************
   1 SI  1.280  1.280  1.280
                                  1 S
                                         4.078E+02 1.543E-01 0.000E+00 0.000E+00
                                         7.428E+01 5.353E-01 0.000E+00 0.000E+00
                                         2.010E+01 4.446E-01 0.000E+00 0.000E+00
                             2-   5 SP
                                         2.319E+01-9.997E-02 1.559E-01 0.000E+00
                                         5.390E+00 3.995E-01 6.077E-01 0.000E+00
                                         1.753E+00 7.001E-01 3.920E-01 0.000E+00
                             6-   9 SP
                                         1.479E+00-2.196E-01 1.059E-02 0.000E+00
                                         4.126E-01 2.256E-01 5.952E-01 0.000E+00
                                         1.615E-01 9.004E-01 4.620E-01 0.000E+00
 *******************************************************************************
The adjoined gaussian exponent is underlined.

The standard Pople scale factor is used for STO-nG basis set when the input scale factor is 0.0. If the input scale factor is 1.0, then the same exponents are attributed to all the atoms of the same row.

 Si, Pople 6-21G split valence basis set

14 4
2 0 6  2.  1.													
2 1 6  8.  1.
2 1 2  4.  1.
2 1 1  0.  1.

*******************************************************************************
   ATOM  X(AU)  Y(AU)  Z(AU)    NO. TYPE  EXPONENT    S COEF     P COEF   D/F/G
 *******************************************************************************
  1 SI  1.280  1.280  1.280
                                  1 S
                                         1.612E+04 1.959E-03 0.000E+00 0.000E+00
                                         2.426E+03 1.493E-02 0.000E+00 0.000E+00
                                         5.539E+02 7.285E-02 0.000E+00 0.000E+00
                                         1.563E+02 2.461E-01 0.000E+00 0.000E+00
                                         5.007E+01 4.859E-01 0.000E+00 0.000E+00
                                         1.702E+01 3.250E-01 0.000E+00 0.000E+00
                             2-   5 SP
                                         2.927E+02-2.781E-03 4.438E-03 0.000E+00
                                         6.987E+01-3.571E-02 3.267E-02 0.000E+00
                                         2.234E+01-1.150E-01 1.347E-01 0.000E+00
                                         8.150E+00 9.356E-02 3.287E-01 0.000E+00
                                         3.135E+00 6.030E-01 4.496E-01 0.000E+00
                                         1.225E+00 4.190E-01 2.614E-01 0.000E+00
                             6-   9 SP
                                         1.079E+00-3.761E-01 6.710E-02 0.000E+00
                                         3.024E-01 1.252E+00 9.569E-01 0.000E+00
                            10-  13 SP
                                         9.334E-02 1.000E+00 1.000E+00 0.000E+00
 *******************************************************************************
The adjoined gaussian exponent is underlined

 Si, Pople 6-21G split valence basis set modified for crystalline calculation

14 4
2 0 6  2.  1.
2 1 6  8.  1.
2 1 2  4.  1.
0 1 1  0.  1.
0.1233392     1.       1.

*******************************************************************************
   ATOM  X(AU)  Y(AU)  Z(AU)    NO. TYPE  EXPONENT    S COEF     P COEF   D/F/G
 *******************************************************************************
   1 SI  1.280  1.280  1.280
                                  1 S
                                         1.612E+04 1.959E-03 0.000E+00 0.000E+00
                                         2.426E+03 1.493E-02 0.000E+00 0.000E+00
                                         5.539E+02 7.285E-02 0.000E+00 0.000E+00
                                         1.563E+02 2.461E-01 0.000E+00 0.000E+00
                                         5.007E+01 4.859E-01 0.000E+00 0.000E+00
                                         1.702E+01 3.250E-01 0.000E+00 0.000E+00
                             2-   5 SP
                                         2.927E+02-2.781E-03 4.438E-03 0.000E+00
                                         6.987E+01-3.571E-02 3.267E-02 0.000E+00
                                         2.234E+01-1.150E-01 1.347E-01 0.000E+00
                                         8.150E+00 9.356E-02 3.287E-01 0.000E+00
                                         3.135E+00 6.030E-01 4.496E-01 0.000E+00
                                         1.225E+00 4.190E-01 2.614E-01 0.000E+00
                             6-   9 SP
                                         1.079E+00-3.761E-01 6.710E-02 0.000E+00
                                         3.024E-01 1.252E+00 9.569E-01 0.000E+00
                            10-  13 SP
                                         1.233E-01 1.000E+00 1.000E+00 0.000E+00
 *******************************************************************************

 Si, Pople 3-21G split valence basis set

14 4
2 0 3  2.  1.
2 1 3  8.  1.
2 1 2  4.  1.
2 1 1  0.  1.

*******************************************************************************
   ATOM  X(AU)  Y(AU)  Z(AU)    NO. TYPE  EXPONENT    S COEF     P COEF   D/F/G
 *******************************************************************************
   1 SI  1.280  1.280  1.280
                                  1 S
                                         9.107E+02 6.608E-02 0.000E+00 0.000E+00
                                         1.373E+02 3.862E-01 0.000E+00 0.000E+00
                                         2.976E+01 6.724E-01 0.000E+00 0.000E+00
                             2-   5 SP
                                         3.667E+01-1.045E-01 1.134E-01 0.000E+00
                                         8.317E+00 1.074E-01 4.576E-01 0.000E+00
                                         2.216E+00 9.514E-01 6.074E-01 0.000E+00
                             6-   9 SP
                                         1.079E+00-3.761E-01 6.710E-02 0.000E+00
                                         3.024E-01 1.252E+00 9.569E-01 0.000E+00
                            10-  13 SP
                                         9.334E-02 1.000E+00 1.000E+00 0.000E+00
 *******************************************************************************

 Si, Pople 3-21G split valence + polarization basis set

14 5
2 0 3  2.  1.
2 1 3  8.  1.
2 1 2  4.  1.
2 1 1  0.  1.
2 3 1  0.  1.

*******************************************************************************
   ATOM  X(AU)  Y(AU)  Z(AU)    NO. TYPE  EXPONENT    S COEF     P COEF   D/F/G
 *******************************************************************************
   1 SI  1.280  1.280  1.280
                                  1 S
                                         9.107E+02 6.608E-02 0.000E+00 0.000E+00
                                         1.373E+02 3.862E-01 0.000E+00 0.000E+00
                                         2.976E+01 6.724E-01 0.000E+00 0.000E+00
                             2-   5 SP
                                         3.667E+01-1.045E-01 1.134E-01 0.000E+00
                                         8.317E+00 1.074E-01 4.576E-01 0.000E+00
                                         2.216E+00 9.514E-01 6.074E-01 0.000E+00
                             6-   9 SP
                                         1.079E+00-3.761E-01 6.710E-02 0.000E+00
                                         3.024E-01 1.252E+00 9.569E-01 0.000E+00
                            10-  13 SP
                                         9.334E-02 1.000E+00 1.000E+00 0.000E+00
                            14-  18 D
                                         4.500E-01 0.000E+00 0.000E+00 1.000E+00
 *****************************************************************************

 Si, user defined basis set derived from Pople 6-21G

14 4
0 0 6 2. 1.
16115.9 	0.00195948
2425.58 	0.0149288
553.867 	0.0728478
156.340 	0.24613
50.0683 	0.485914
17.0178 	0.325002
0 1 6 8. 1.
292.718 	-0.0027809 	0.0044383
69.8731 	-0.0357146 	0.0326679
22.3363 	-0.114985 	0.134721
8.15039 	0.0935634 	0.328678
3.13458 	0.603017 	0.449640
1.22543 	0.418959 	0.261372
0 1 2 4. 1.
1.07913 	-0.376108 	0.067103
0.302422 	1.25165 	0.956883
0 1 1 0. 1.
0.123 		1. 		1.

 *******************************************************************************
   ATOM  X(AU)  Y(AU)  Z(AU)    NO. TYPE  EXPONENT    S COEF     P COEF   D/F/G
 *******************************************************************************
   1 SI  1.280  1.280  1.280
                                  1 S
                                         1.612E+04 1.959E-03 0.000E+00 0.000E+00
                                         2.426E+03 1.493E-02 0.000E+00 0.000E+00
                                         5.539E+02 7.285E-02 0.000E+00 0.000E+00
                                         1.563E+02 2.461E-01 0.000E+00 0.000E+00
                                         5.007E+01 4.859E-01 0.000E+00 0.000E+00
                                         1.702E+01 3.250E-01 0.000E+00 0.000E+00
                             2-   5 SP
                                         2.927E+02-2.781E-03 4.438E-03 0.000E+00
                                         6.987E+01-3.571E-02 3.267E-02 0.000E+00
                                         2.234E+01-1.150E-01 1.347E-01 0.000E+00
                                         8.150E+00 9.356E-02 3.287E-01 0.000E+00
                                         3.135E+00 6.030E-01 4.496E-01 0.000E+00
                                         1.225E+00 4.190E-01 2.614E-01 0.000E+00
                             6-   9 SP
                                         1.079E+00-3.761E-01 6.710E-02 0.000E+00
                                         3.024E-01 1.252E+00 9.569E-01 0.000E+00
                            10-  13 SP
                                         1.230E-01 1.000E+00 1.000E+00 0.000E+00
 ******************************************************************************

Si Basis set AO  exponent Total energy bulk silicon SCF cycles Million. biel integrals CPU integrals CPU total

sto-3g   

9 0.1315

   -5.713207531E+02   

8

0.11 2.46 3.22

3-21   

13 0.09334

   -5.748914299E+02   

 9

0.86 26.38 28.70

3-21+d   

18 0.09334

   -5.749481876E+02   

 9

2.04 53.19 57.70

6-21   

13 0.09334

   -5.778250380E+02   

10

0.92 30.04 32.75

6-21mod   

13 0.1233

   -5.778265558E+02   

 9

0.58 12.80 14.75

free.out   

13 0.123

   -5.778265813E+02   

 9

0.58 12.81 14.74

The table shows for bulk Silicon how  the value of the exponent of the lowest exponent gaussian influence the computational resources and the total energy, when all other computational parameters are fixed. The crystalline basis functions are the Bloch functions, built with localized functions, the AOs. The diffuse functions, very important to describe the tails of the electron density in a molecular systems, are useless in an infinite system, increase the computational cost, but do not improve the wave function.
Crystalline atomic basis sets are built starting from an atomic basis set optimized for molecules, and reoptimizing the exponent of the most diffuse GTF.