25.2.1 Keywords for System Specification

General information defining the molecular system: nuclear coordinates, symmetry, basis functions, number of occupied MOs, etc. which are required by every module.

$title

give title of run or project here.

$symmetry d4h

Schönflies symbol of the point group. define, dscf, grad, ridft, rdgrad, odft, escf, egrad, statpt, relax, and freeh support all point groups. mpshift and aoforce support for NMR shielding and force constant calculations etc. all those groups that do not have complex irreps ($C_3$, $C_3h$, $T$, etc). Use a lower symmetry group in this case. For all other programs see the respective chapters above.

$atoms

Example with the same basis set on all atoms:

 
$atoms
   basis = def2-SV(P)

An example with mixed basis sets and ECPs:

 
$atoms
   basis =def2-SV(P)
cu 1-4    
   basis =cu ecp-18 arep   
   jbas  =cu ecp-18       
   ecp   =cu ecp-18 arep
se 5-6  
   basis =se ecp-28 arep dzp 
   jbas  =se ecp-28         
   ecp   =se arep

For each atom group, one can specify

the basis set
and the auxiliary (fitting) basis sets (jbas, jkbas, cbas, cabs, xbas)
the ECP if this is used,
the mass (mass), and
the charge (charge).

Additionally, the isotopes and the gyromagnetic ratio can be defined, e.g. for $^{3}$H with a ratio of 28.534986500,

 h  3
     ncisotope=    3  
     gyromag=   28.534986500

Here, the given isotopes and the gyromagnetic ratio are used for the calculation of NMR coupling constants or EPR hyperfine couplings. By default, we assume the most common isotopes for NMR and EPR spectroscopy.

Attributes listed immediately below $atoms are used as defaults which are assigned to all atoms for which these attributes are not overwritten by subsequent assignments to specific atom groups. In this section the basis set name should not be preceeded by an atom symbol. In setting for specific atoms groups the basis set names should be preceeded by the atom symbols. Where no other specifications are made in $atoms, the following defaults are used:

auxiliary basis sets will be assigned automatically if needed based on the name of the orbital basis if available in the basis set library or the control file,
the atomic masses are by default set to isotopic averages,
the charges are determined from the atomic symbols.
for basis sets with names starting with def-, def2-, or dhf-, or ending with -PP and for the LANL2DZ basis sets the corresponding default ECPs will automatically added for atoms heavier than Kr if no other ECPs have been specified similar as it is done by define.

Definitions of (auxiliary) basis sets and ECPs can be provided in files with names specified in the data groups $basis, $jbas, $cbas, $cabs, $jkbas, $xbas, and $ecp. If no definitions are provided the respective information will be searched in the basis set libraries and then stored in the files basis, ecp and auxbasis.

$pople char

This data group specifies the number of Cartesian components of basis functions (i.e. 5d and 7f in AO-Basis, 6d and 10f in CAO-Basis) for which the SCF calculation should be performed. Possible values for char are AO (default) or CAO. This keyword should usually be set in accordance with the chosen basis set. Most basis sets are defined with only the pure spherical components. This is the case for all Karlsruhe basis sets, the correlation consistent basis set families cc-pVXZ etc., and many other basis sets. An exception are the 6-31G basis sets: the polarization functions for them (i.e. for 6-31G*, 6-31G**, and the corresponding basis sets with diffuse functions indicated with an additional $+$ or $++$) are defined as full Cartesian set and should be used with $pople CAO.