7.3 Basis Set Symbolic Representation

Examples are given in the tables below and follow the standard format generally adopted for specifying basis sets. The single exception applies to additional diffuse functions. These are best inserted in a similar manner to the polarization functions; in parentheses with the light atom designation following heavy atom designation. (i.e., heavy, light). Use a period (.) as a place-holder (see examples).

	$j$	$k$	$l$	$m$	$n$
$\ensuremath{\mathrm{STO}}\! -\! j(k+,l+)\ensuremath{\mathrm{G}}(m,n) \; \; \;$	2,3,6 $\;$	$^ a \;$	$^ b \;$	$d \; \; \;$	$p$
$j\! -\! 21(k+,l+)\ensuremath{\mathrm{G}}(m,n) \; \; \;$	3 $\;$	$^ a \;$	$^ b \;$	$2d \; \; \;$	$2p$
$j\! -31(k+,l+)\ensuremath{\mathrm{G}}(m,n) \; \; \;$	4,6 $\;$	$^ a \;$	$^ b \;$	$3d \; \; \;$	$3p$
$j-311(k+,l+)\ensuremath{\mathrm{G}}(m,n) \; \; \;$	6 $\;$	$^ a \;$	$^ b \;$	$df$ , $2df$ , $3df \; \; \;$	$pd$ , $2pd$ , $3pd$

Table 7.1: Summary of Pople type basis sets available in Q-Chem. $m$ and $n$ refer to the polarization functions on heavy and light atoms respectively. $^ ak$ is the number of sets of diffuse functions on heavy $^ bl$ is the number of sets of diffuse functions on light atoms.

Symbolic Name	Atoms Supported
STO-2G	H, He, Li $\to$ Ne, Na $\to$ Ar, K, Ca, Sr
STO-3G	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Kr, Rb $\to$ Sb
STO-6G	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Kr
3-21G	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Kr, Rb $\to$ Xe, Cs
4-31G	H, He, Li $\to$ Ne, P $\to$ Cl
6-31G	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Zn
6-311G	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr
G3LARGE	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Kr
G3MP2LARGE	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr

Table 7.2: Atoms supported for Pople basis sets available in Q-Chem (see the Table below for specific examples).

Symbolic Name	Atoms Supported
3-21G	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Kr, Rb $\to$ Xe, Cs
3-21+G	H, He, Na $\to$ Cl, Na $\to$ Ar, K, Ca, Ga $\to$ Kr
3-21G*	H, He, Na $\to$ Cl
6-31G	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Zn, Ga $\to$ Kr
6-31+G	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr
6-31G*	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Zn, Ga $\to$ Kr
6-31G(d,p)	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Zn, Ga $\to$ Kr
6-31G(.,+)G	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr
6-31+G*	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr
6-311G	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr
6-311+G	H, He, Li $\to$ Ne, Na $\to$ Ar
6-311G*	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr
6-311G(d,p)	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr
G3LARGE	H, He, Li $\to$ Ne, Na $\to$ Ar, K $\to$ Kr
G3MP2LARGE	H, He, Li $\to$ Ne, Na $\to$ Ar, Ga $\to$ Kr

Table 7.3: Examples of extended Pople basis sets.

	SV $(k+,l+)(md,np)$ , DZ $(k+,l+)(md,np)$ , TZ $(k+,l+)(md,np)$
$k$	# sets of heavy atom diffuse functions
$l$	# sets of light atom diffuse functions
$m$	# sets of d functions on heavy atoms
$n$	# sets of p functions on light atoms

Table 7.4: Summary of Dunning-type basis sets available in Q-Chem.

Symbolic Name	Atoms Supported
SV	H, Li $\to$ Ne
DZ	H, Li $\to$ Ne, Al $\to$ Cl
TZ	H, Li $\to$ Ne

Table 7.5: Atoms supported for old Dunning basis sets available in Q-Chem.

Symbolic Name	Atoms Supported
SV	H, Li $\to$ Ne
SV*	H, B $\to$ Ne
SV(d,p)	H, B $\to$ Ne
DZ	H, Li $\to$ Ne, Al $\to$ Cl
DZ+	H, B $\to$ Ne
DZ++	H, B $\to$ Ne
DZ*	H, Li $\to$ Ne
DZ**	H, Li $\to$ Ne
DZ(d,p)	H, Li $\to$ Ne
TZ	H, Li $\to$ Ne
TZ+	H, Li $\to$ Ne
TZ++	H, Li $\to$ Ne
TZ*	H, Li $\to$ Ne
TZ**	H, Li $\to$ Ne
TZ(d,p)	H, Li $\to$ Ne

Table 7.6: Examples of extended Dunning basis sets.

Symbolic Name	Atoms Supported
cc-pVDZ	H, He, B $\to$ Ne, Al $\to$ Ar, Ga $\to$ Kr
cc-pVTZ	H, He, B $\to$ Ne, Al $\to$ Ar, Ga $\to$ Kr
cc-pVQZ	H, He, B $\to$ Ne, Al $\to$ Ar, Ga $\to$ Kr
cc-pCVDZ	B $\to$ Ne
cc-pCVTZ	B $\to$ Ne
cc-pCVQZ	B $\to$ Ne
aug-cc-pVDZ	H, He, B $\to$ Ne, Al $\to$ Ar, Ga $\to$ Kr
aug-cc-pVTZ	H, He, B $\to$ Ne, Al $\to$ Ar, Ga $\to$ Kr
aug-cc-pVQZ	H, He, B $\to$ Ne, Al $\to$ Ar, Ga $\to$ Kr
aug-cc-pCVDZ	B $\to$ F
aug-cc-pCVTZ	B $\to$ Ne
aug-cc-pCVQZ	B $\to$ Ne

Table 7.7: Atoms supported Dunning correlation-consistent basis sets available in Q-Chem.

Symbolic Name	Atoms Supported
TZV	Li $\to$ Kr
VDZ	H $\to$ Kr
VTZ	H $\to$ Kr

Table 7.8: Atoms supported for Ahlrichs basis sets available in Q-Chem.

Symbolic Name	Atoms Supported
pc-0, pc-1, pc-2, pc-3, pc-4	H $\to$ Ar
pcJ-0, pcJ-1, pcJ-2, pcJ-3, pcJ-4	H $\to$ Ar, except Li, Be, Na, Mg
pcS-0, pcS-1, pcS-2, pcS-3, pcS-4	H $\to$ Ar

Table 7.9: Atoms supported for Jensen polarization consistent basis sets available in Q-Chem.

7.3.1 Customization

Q-Chem offers a number of standard and special customization features. One of the most important is that of supplying additional diffuse functions. Diffuse functions are often important for studying anions and excited states of molecules, and for the latter several sets of additional diffuse functions may be required. These extra diffuse functions can be generated from the standard diffuse functions by applying a scaling factor to the exponent of the original diffuse function. This yields a geometric series of exponents for the diffuse functions which includes the original standard functions along with more diffuse functions.

When using very large basis sets, especially those that include many diffuse functions, or if the system being studied is very large, linear dependence in the basis set may arise. This results in an over-complete description of the space spanned by the basis functions, and can cause a loss of uniqueness in the molecular orbital coefficients. Consequently, the SCF may be slow to converge or behave erratically. Q-Chem will automatically check for linear dependence in the basis set, and will project out the near-degeneracies, if they exist. This will result in there being slightly fewer molecular orbitals than there are basis functions. Q-Chem checks for linear-dependence by considering the eigenvalues of the overlap matrix. Very small eigenvalues are an indication that the basis set is close to being linearly dependent. The size at which the eigenvalues are considered to be too small is governed by the $rem variable BASIS_LIN_DEP_THRESH. By default this is set to 6, corresponding to a threshold of $10^{-6}$ . This has been found to give reliable results, however, if you have a poorly behaved SCF, and you suspect there maybe linear dependence in you basis, the threshold should be increased.

PRINT_GENERAL_BASIS

Controls print out of built in basis sets in input format

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE

Print out standard basis set information

FALSE

Do not print out standard basis set information

RECOMMENDATION:

Useful for modification of standard basis sets.

BASIS_LIN_DEP_THRESH

Sets the threshold for determining linear dependence in the basis set

TYPE:

INTEGER

DEFAULT:

6

Corresponding to a threshold of $10^{-6}$

OPTIONS:

$n$

Sets the threshold to $10^{-n}$

RECOMMENDATION:

Set to 5 or smaller if you have a poorly behaved SCF and you suspect linear dependence in you basis set. Lower values (larger thresholds) may affect the accuracy of the calculation.

TRUE	Print out standard basis set information
FALSE	Do not print out standard basis set information