Vibrational frequencies

The calculation of vibrational frequencies are controlled by the keyword .VIBANA. Thus, in order to calculate the vibrational frequencies of a molecule, all that is is needed is the input:

**DALTON INPUT
.RUN PROPERTIES
**WAVE FUNCTIONS
.HF
**PROPERTIES
.VIBANA
**END OF DALTON INPUT

This keyword will, in addition to calculating the molecular frequencies, also calculate the zero-point vibrational energy corrections and vibrational and rotational partition functions at selected temperatures.

DALTON evaluates the molecular Hessian in Cartesian coordinates, and the vibrational frequencies of any isotopically substituted species may therefore easily be obtained on the basis of the full Hessian. Thus, if we would like to calculate the vibrational frequencies of isotopically substituted molecules, this may be obtained through an input like:

**DALTON INPUT
.RUN PROPERTIES
**WAVE FUNCTIONS
.HF
**PROPERITES
.VIBANA
*VIBANA
.ISOTOP
   2   5
 1 2 1 1 1
 2 1 1 1 1
**END OF DALTON INPUT

The keyword .ISOTOP in the *VIBANA input module indicates that more than only the isotopic species containing the most abundant isotopes are to be calculated, which will always be calculated. The numbers on the second line denotes the number of isotopically substituted species that is requested and the number of atoms in the system. The following lines then lists the isotopic constitution of each of these species. 1 corresponds to the most abundant isotope, 2 corresponds to the second most abundant isotope and so on. The isotopic substitution have to be given for all atoms in the molecule (not only the symmetry independent), and the above input could for instance correspond to a methane molecule, with the isotopic species $CH_3D$ and $^{13}CH_4$.

As the isotopic substitution of all atoms in the molecule has to be specified, let us mention the way symmetry-dependent atoms will be generated. The atoms will be grouped in symmetry-dependent atom blocks. The specified symmetry-independent atom will be the first of this block, and the symmetry-dependent atoms will be generated according to the order of the symmetry elements. Thus, assuming D$_{2h}$ symmetry with symmetry generating elements X Y Z, the atoms generated will come in the order X, Y, XY, Z, XZ, YZ, and XYZ.