WINOPTACT: a computer program to calculate optical rotatory power and refractive indices from crystal structure data

Abstract

2. Description The original OPTACT program needed all the atoms in the unit cell to be entered manually, but WINOPTACT calculates them from the space group, unit-cell parameters and atoms in the asymmetric unit. In addition, the structure data can be read in directly from a CIF. Each atom is assigned an isotropic polarizability value. Other parameters that need to be specified are the wavelength of light and an approximate average refractive index for the crystal. All the initial parameters appear automatically in a window. The menu item ‘Go’ then carries out the calculation and results are written to another window. The results include values for the optical rotatory power, refractive indices, birefringence and gyration tensor components. In addition, anisotropic polarizability ellipsoid components are computed for each atom, resulting from the influence of the local fields around each atom. A new feature of the program is that an atom can be selected and the input polarizability can be automatically changed in steps to investigate how the refractive indices and optical rotation vary with polarizability. The results are tabulated in a window and can also be plotted graphically by the program.