Vibrational frequencies

 

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

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

This keyword will, in addition to calculating the molecular frequencies and rotational constants, also calculate the zero-point vibrational energy correction  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
 1 2 1 1 1
 2 1 1 1 1
*END OF 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 always will be calculated. The number on the second line denotes the number of isotopically substituted species that is wanted. The following line 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 and .

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 symmetry with symmetry generating elements X Y Z, the atoms generated will come in the order X, Y, XY, Z, XZ, YZ, and XYZ.