Users may, on occasion, prefer to use nonstandard basis, and it is possible to declare userdefined basis sets in QChem input (see Chapter 3 on QChem inputs). The format for inserting a nonstandard userdefined basis set is both logical and flexible, and is described in detail in the job control section below.
Note that the SAD guess is not currently supported with nonstandard or userdefined basis sets. The simplest alternative is to specify the GWH or CORE options for SCF_GUESS, but these are relatively ineffective other than for small basis sets. The recommended alternative is to employ basis set projection by specifying a standard basis set for the BASIS2 keyword. See the section in Chapter 4 on initial guesses for more information.
In order to use a userdefined basis set the BASIS $rem must be set to GENERAL or GEN.
When using a nonstandard basis set which incorporates or higher angular momentum basis functions, the $rem variable PURECART needs to be initiated. This $rem variable indicates to the QChem program how to handle the angular form of the basis functions. As indicated above, each integer represents an angular momentum type which can be defined as either pure (1) or Cartesian (2). For example, 111 would specify all , and basis functions as being in the pure form. 121 would indicate  and  functions are pure and functions Cartesian.
PURECART
INTEGER
TYPE:
Controls the use of pure (spherical harmonic) or Cartesian angular forms
DEFAULT:
2111
Cartesian functions and pure functions
OPTIONS:
Use 1 for pure and 2 for Cartesian.
RECOMMENDATION:
This is predefined for all standard basis sets
In standard basis sets all functions are pure, except for the functions in 21G–type bases (e.g., 321G) and 31G bases (e.g., 631G, 631G*,631+G*, ). In particular, the 6311G series uses pure functions for both and .
The format for the userdefined basis section is as follows:
$basis
0
****
$end
where

Atomic symbol of the atom (atomic number not accepted) 

Angular momentum symbol (S, P, SP, D, F, G) 

Degree of contraction of the shell (integer) 

Scaling to be applied to exponents (default is 1.00) 

Gaussian primitive exponent (positive real number) 

Contraction coefficient for each angular momentum (nonzero 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 one required for compound shells like SP. As with all QChem input deck information, all input is caseinsensitive.
Example 7.177 Example of adding a userdefined nonstandard basis set. Note that since , and 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 userdefined general basis BASIS2 sto3g sto3g 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 0.0494720 0.511541 0.493363 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