8.4 User-Defined Basis Sets ($basis)8.4.2 Job Control 8.5 Mixed Basis Sets

8.4.3 Format for User-Defined Basis Sets

(September 23, 2025)

The format for the user-defined basis section is as follows:

$basis

$X$ 0

$L$ $K$ $s c a l e$

$\alpha_{1}$ $C_{1}^{L_{\text{min}}}$ $C_{1}^{L_{\text{min}}+1}$ $\ldots$ $C_{1}^{L_{\text{max}}}$

$\alpha_{2}$ $C_{2}^{L_{\text{min}}}$ $C_{2}^{L_{\text{min}}+1}$ $\ldots$ $C_{2}^{L_{\text{max}}}$

$\vdots$ $\vdots$ $\vdots$ $\ddots$ $\vdots$

$\alpha_{K}$ $C_{K}^{L_{\text{min}}}$ $C_{K}^{L_{\text{min}}+1}$ $\ldots$ $C_{K}^{L_{\text{max}}}$

****

$end

where

$X$	Atomic symbol of the atom (atomic number not accepted)
$L$	Angular momentum symbol (S, P, SP, D, F, G)
$K$	Degree of contraction of the shell (integer)
$s c a l e$	Scaling to be applied to exponents (default is 1.00)
$\alpha_{i}$	Gaussian primitive exponent (positive real number)
$C_{i}^{L}$	Contraction coefficient for each angular momentum (non-zero real numbers).

Atoms are terminated with **** and the complete basis set is terminated with the $end keyword terminator. No blank lines can be incorporated within the general basis set input. Note that more than one contraction coefficient per line is required for compound shells like SP. As with all Q-Chem input deck information, all input is case-insensitive.

Example 8.1 Example of adding a user-defined non-standard basis set. Note that since $d$ , $f$ and $g$ functions are incorporated, the $rem variable PURECART must be set. Note the use of BASIS2 for the initial guess.

$molecule
   0  1
   O
   H  O  oh
   H  O  oh  2  hoh

   oh  =   1.2
   hoh = 110.0
$end

$rem
   EXCHANGE   hf
   BASIS      gen      user-defined general basis
   BASIS2     sto-3g   sto-3g orbitals as initial guess
   PURECART   112      Cartesian d functions, pure f and g
$end

$basis
   H  0
   S  2  1.00
      1.30976    0.430129
      0.233136   0.678914
****
   O  0
   S  2  1.00
      49.9810    0.430129
      8.89659    0.678914
   SP 2  1.00
      1.94524    0.049472    0.511541
      0.49336    0.963782    0.612820
   D  1  1.00
      0.39000    1.000000
   F  1  1.00
      4.10000    1.000000
   G  1  1.00
      3.35000    1.000000
****
$end

$basis
	$X$	0
	$L$	$K$	$s c a l e$
	$\alpha_{1}$	$C_{1}^{L_{\text{min}}}$	$C_{1}^{L_{\text{min}}+1}$	$\ldots$	$C_{1}^{L_{\text{max}}}$
	$\alpha_{2}$	$C_{2}^{L_{\text{min}}}$	$C_{2}^{L_{\text{min}}+1}$	$\ldots$	$C_{2}^{L_{\text{max}}}$
	$\vdots$	$\vdots$	$\vdots$	$\ddots$	$\vdots$
	$\alpha_{K}$	$C_{K}^{L_{\text{min}}}$	$C_{K}^{L_{\text{min}}+1}$	$\ldots$	$C_{K}^{L_{\text{max}}}$
****
$end

Search Results

8.4.3 Format for User-Defined Basis Sets