= Define your own basis set =

Example of basis format (6-31G basis):

{{{
****
H   1   0   
S    4    2   
      18.73113700
       2.82539370
       0.64012170
       0.16127780
  0.03349460  0.00000000
  0.23472695  0.00000000
  0.81375733  0.00000000
  0.00000000  1.00000000
****
Li   3   1   
S   10    3   
     642.41892000
      96.79851500
      22.09112100
       6.20107030
       1.93511770
       0.63673580
       2.32491840
       0.63243060
       0.07905340
       0.03596200
  0.00214260  0.00000000  0.00000000
...
}}}
If the number of contraction is 0, it means uncontracted basis functions for the given L number, and the contraction coefficients (corresponding to a unit matrix) are not provided.

Example of ECP basis functions (SBKJC-VDZ):

{{{
****
Li      3    1
S       4    2
            0.61770000
            0.14340000
            0.05048000
            0.01923000
    -0.1628700000     0.0000000000
     0.1264300000     0.0000000000
     0.7617900000     0.0000000000
     0.0000000000     0.2180000000
P       4    2
            0.61770000
            0.14340000
            0.05048000
            0.01923000
     0.0620500000     0.0000000000
     0.2471900000     0.0000000000
     0.5214000000     0.0000000000
     0.0000000000     0.3429000000
ECP
Li     2    1
P potential  1
 1       1.34306000      -0.73063000
S potential  2
 0       0.61284000       1.80131000
 2       1.64881000       3.54971000
****
...
}}}

Example of spin-orbit ECP (also called 2-component ECP) basis functions (Pitzer-VDZ-PP):

{{{
****
Li      3    2
S       4    3
            3.88900000
            0.57250000
            0.07190000
            0.02743000
    -0.0089028000     0.0000000000     0.0000000000
    -0.1377106000     0.0000000000     0.0000000000
     0.5955815000     0.0000000000     1.0000000000
     0.4961206000     1.0000000000     0.0000000000
P       4    2
            1.52100000
            0.27380000
            0.07342000
            0.02399000
     0.0229010000     0.0000000000
     0.1395965000     0.0000000000
     0.5007982000     0.0000000000
     0.5074542000     1.0000000000
D       1    1
            0.11750000
     1.0000000000
ECP
Li     2    1    1
P potential  3
   2      0.80780000000000     -0.11866700000000
   2      2.55000000000000     -1.21779400000000
   1      7.25350000000000     -1.37580500000000
S potential  4
   2      0.79980000000000     24.33369900000000
   2      0.77410000000000    -20.66639700000000
   1      1.19430000000000     -1.14289200000000
   0      2.19990000000000      2.99401900000000
P so-potential  3
   2      0.80780000000000      0.00007000000000
   2      2.55000000000000     -0.00032000000000
   1      7.25350000000000      0.00173800000000
****
...
}}}

'''NOTE:''' in the literature the coefficients of the so-potentials are NOT always defined in the same manner. BDF assumes that the so-potentials have been multiplied by 2/L, being in line with the manner of most of the other quantum chemistry programs.

To use your own basis that is not included in the '''bdf-pkg/basis_library''', you can create a file  '''''XXX ''''' containing your basis  '''''in the same directory of the input and run script ''''', and then you can just specify the basis in COMPASS like the normal basis by the name '''XXX'''.


== Download basis set from EMSL basis set exchange and convert to BDF basis set format ==
You can download basis set from EMSL basis set exchange (https://www.basissetexchange.org/). You should output basis set as BDF format and save it in a file.

'''NOTE:''' the ECP basis sets from EMSL need to be modified manually.