A new method is presented for calculating optical properties within the framework of the self consistent Linear Muffin Tin Orbital (LMTO) band structure theory. We show how Green’s second identity along with the commutation relation between the position and Hamiltonian operators may be used to calculate the velocity matrix elements required for optical properties. The method has beed applied to calculate the imaginary part of the dielectric constant for $FeSi$ and $Si$. At present we are extending the theory for nonlinear interactions in which a nonlocal Hamiltonian has been included.

The structural and electronic characterization of thieno [3,4-b][1,4] diazepine and 1,5-benzodiazepine systems was carried out by semiempirical quantum mechanical calculations. A number of electronic properties were computed and examined in order to study the structure-activity relationship. Theoretical data indicate that the electronic rather than structural properties appear primarily responsible for the variant degree of anticonvulsant activity exhibited by compounds 1-4.

By considering the fusion process of two exciton-polaritons to a third in the upper polariton branch, we describe the frequency dependence of two photon absorption near a dipole allowed exciton state in a Q. W. Two photon absorption as a function of the two photon excitation energy shows a lorentzian profile centered along the polariton dispersion.

The results of self-consistent linear muffin-tin orbital calculations for the ordered end memhers of the $FeSi_1_+_x$ series, i.e. FeSi (x=O) with CsCl structure and $\alpha-FeSi_2$ and $\gamma-FeSi_2 (x=l)$ with tetragonal and cubic fluorite structure respectively, predict semimetallic behaviour for FeSi and metallic behaviour and higher stability for $\alpha-FeSi_2$ and $\gamma-FeSi_2$. The valence band density of states (D.O.S.) features of the $\alpha-FeSi_2$ differ only slightly from those of the cubic fluorite ($\gamma-FeSi_2$). The analysis of the valence band photoemission spectra taken on silicide thin films epitaxially grown on Si (111) substrates can, therefore, only estimate the composition of the mono and disilicide phases present in the annealed films, but cannot distinguish between $\alpha-FeSi_2$ and $\gamma-FeSi_2$.

The LMTO-ASA codes, modified and optimized to run on a low-cost RISC workstation, have been used to calculate the energy band structure and the electronic density of states of $CoSi_2$. Crystal field effects on core states were included and in the calculation was required the self-consistence on total charge densities, $E_v$ and potential parameters. The results are in good agreement with the experiment and other theoretical calulations.