3.1 Writing simple input files (withdout using define)

For standard non-relativistic DFT (or HF-SCF) ground-state calculations, TURBOMOLE requires only a minimal input:

generate your atomic coordinates by any tool you are familiar with, save it as an .xyz file (xyz is a file format for coordinates) and use the TURBOMOLE script x2t to convert the .xyz file into the TURBOMOLE format:
x2t xyzinputfile > coord
or use a conversion tool like babel:
babel -i input-type -o tmol coord
where input-type should be babel’s abbreviation for the format of your input file.

generate then the control file with, e.g., the following content:

 
          $atoms
             basis = def2-SV(P)
          $coord file=coord
          $dft
             funtional b-p
             grid m3
          $end

you can then start either a single-point calculation with

          dscf > dscf.out

or a geometry optimization with

           jobex

if you want to use the RI-J approximation (ridft) add a line with $rij. In that case single-point calculations should be started with
```
          ridft > ridft.out
        
```
and geometry optimizations with
```
           jobex -ri
        
```
for vibrational frequencies and IR intensities invoke after a converged geometry optimization the program aoforce:
aoforce > aoforce.out

you can optionally include a title line that will be printed in the outputs

           $title
               DFT/B-P/def2-SV(P) for MyMolecule

The DFT and HF-SCF programs dscf and ridft will automatically detect the molecular point group from the provided coordinates and exploit the point group symmetry.

By default the programs will determine start orbitals and orbital energies by diagonalizing a Fock matrix constructed with a superposition of spherical atomic densities and determine an orbital occupation for the (neutral) molecule based on the Aufbau principle with these orbital energies.

If you want to do a calculation on a charged species or for a different number of unpaired electrons, or, more precisely, a different minor spin quantum number $M_S$, this can be specified in the control file with:
$atomdens total_charge=$n$ unpaired=$m$
where $n$ and $m$ have to be integer numbers and $m$ has to be positive.

Alternatively, you can use any of the other available options to define the orbital occupations and generate start orbitals (see Sec. 25.2.2).

The Cartesian positions of atoms can be fixed by adding in the $coord data group a f behind the atom symbol:

     $coord
       0.000   0.000  -0.764 o f
       1.500   0.000   0.382 h f
      -1.500   0.000   0.368 h

Some basis sets require for heavier atoms the addition of effective core potentials (ECPs). This can be done as follows:

     $atoms
        basis = dhf-SVP-2c
     pb 2-4,7
        ecp   = pb dhf-ecp-2c

Some old basis sets from Pople and coworkers (e.g. 6-31G(d)) should be used with 6-component, i.e. cartesian, d-functions, while TURBOMOLE’s default is to use 5-component spherical d-functions. The use of 6 component d-functions and the full spherical sets for higher angular momentum functions can be requested by adding the keyword

   $pople CAO

For the additional input needed for post-HF or post-KS calculations please see the following sections and chapters.

3.1.1 Symmetry handling

As mendioned above, the dscf and ridft programs per default automatically detect the molecular point group from the provided coordinates. If symmetry elements are found, the molecular structure will be shifted and rotated into the standard orientation needed for the detected point group (e.g. the main rotation axis aligned with the $z$ axis).

If a calculation should for any reason not use the full molecular point group, the point group actually used in the calculation can be set in the control file with:
$symmetry sflies
where sflies should be the Schönflies symbol in lower case letters without using any special symbol to indicate lower indices, i.e. c2v for C$_{2v}$. Note, however, that for these cases the coordinates that you provide have to be for the standard orientation expected by TURBOMOLE.

With the option
$symmetry nondeg
The automatic symmetry detection is restricted to D$_{2h}$ and its subgroups which have only non-degenerated irreps. This is in particular useful for two cases:

Post-SCF methods as e.g. CCSD or the calculation of excitation energies and response properties with ricc2 which are only implemented for D$_{2h}$ and its subgroups.
Highly symmetric open-shell systems, most prominently atoms and atomic ions, where UHF calculations without fractional occupations are sometimes only possible in a subgroup of the full molecular point group that enforces less or no symmetry-degeneracies.

With c1 the use of point group symmetry is disabled.

Pitfalls: coordinate orientation and B irreps

As mentioned above, the automatic symmetry detection of TURBOMOLE rotates molecular structures into a standard orientation that is compatible with the detected molecular point group, which implies in particular that the (or one of the) main rotation axis is aligned with the z axis of the coordinate system.

For some molecular point groups this is, however, not sufficient to make the assignment of symmetry-adapted objects like (canonical) molecular orbitals, electronic excitations, normal modes, etc. to the irreducible representations unique. This affects the enumeration of the irreps $B_i$ in $D_{2n}$ and $C_{2nv}$ ($n = 1, 2, 3, \ldots$) and the irreps $B_{ig}$ and $B_{iu}$ in $D_{2nh}$: For them, the index $i$ depends either on the precise choice of the main rotation (z) axis ($D_{2}$ and $D_{2h}$) or the orientation of the structure in the $xy$ plane, i.e. the choice of $\sigma_v$ and $\sigma_d$ mirror planes in $C_{2nv}$ and $D_{2nh}$ and/or the choice of the $C_2'$ and $C_2''$ axis in $D_{2n}$ and $D_{2nh}$. For additional information see recommendations 4 and 5 a-d in JCP 23 (1955) 1997–2011 (Ref. ).

For the important class of planar molecules in $C_{2v}$, $D_{2h}$, $D_{4h}$, and $D_{6h}$ TURBOMOLE’s automatic symmetry-detection in define, dscf, and ridft selects (for release versions beyond V7.9) automatically the orientation specified in recommendations 5 a-c of Ref. :

$C_{2v}$: planar molecules are located in the $yz$ plane and the $x$ axis perpendicular to the plane of the molecule (Rec. 5a)
$D_{2h}$: planar molecules are located in the $yz$ plane with the $z$ axis chosen such that it passes through the greatest number of atoms (Rec. 5b)
$D_{4h}$, $D_{6h}$: planar molecules are located in the $xy$ plane and oriented such that the $C_2'$ (aligned with the $x$ axis) runs through the larger number of atoms and $C_2''$ through the smaller number of atoms

Different orientations are accepted, if the molecular point group is set by the user in $symmetry and the molecular structure in $coord has already an orientation that is compatible with the molecular point group.

3.1.2 Geometry optimizations

Geometry optimizations on molecular (i.e. non-periodic) systems are by default done in internal redundant coordinates that will be generated automatically by the optimizer statpt when it is invoked for the first time. If you want to set up different internal coordinates or if you want to freeze internal coordinates you can do this with the input generator define (vide infra).

For geometry optimizations in cartesians coordinates you need to disable the use of internal coordinates by setting the data group $optimize accordingly (vide infra).