Optical Rotation

The calculation of optical rotation is a special case of the calculation of Vibrational Raman Optical Activity (see Sec. 11.4), as the tensor determining the optical rotation, the mixed electric-magnetic polarizability, also contributes to vibrational Raman optical activity, although in the latter case it is the geometrical derivatives of the tensor which are the central quantities.

Many of the comments made regarding basis set requirments for VROA calculations will thus also be applicable for the calculation of optical. However, we note that a very extensive basis set investigation of the optical rotation have been presented [86]. A typical input for the calculation of optical rotation would be:

**DALTON INPUT
.RUN PROPERTIES
**WAVE FUNCTIONS
.HF
**PROPERTIES
.OPTROT
*ABALNR
.FREQUENCY
 2
 0.001 0.077318
.THRESH
 1.0D-4
**END OF DALTON INPUT

DALTON will always calculate the optical rotation both with and without London atomic orbitals as this has a negligible computational cost compared to the calculation using London atomic orbitals only, since we will anyway have to solve only three response equations corresponding to the perturbing electric field. The optical rotation will only be observed for molecules without symmetry, and by definition the optical rotation will be zero in the static limit. One can approximate the static limit by supplying the program with a very large wavelength (small frequency), as in the example above, in order to be able to compare with approximations that are only valid in the static limit [87,86].