An embedded-molecular-cluster method for calculating the electronic structure of point defects in non-metallic crystals. II. Structural elements in the form of molecules

Abstract

For pt.I see ibid., vol.21, p.5041 (1988). The embedded-molecular-cluster method, as proposed in the authors previous paper for the calculation of the electronic structure of point defects in non-metallic crystals, has been applied in the present work for the case of crystals containing structural elements in the shape of rigid molecules, molecular ions, etc. Using the Green function of perfect-crystal lattice dynamics, equations have been obtained describing polarisation of the remainder of the crystal. The operator V^eff, which accounts for exchange and Coulomb interaction between the cluster and the rest of the crystal, including its polarisation, and is an addition to the Hartree-Fock operator, has been evaluated. Both problems (calculation of polarisation of the rest of the crystal and the solution of the effective Schrodinger equation for the cluster) have to be solved in a self-consistent way. Parameterisation effected for the method has made it possible to express explicitly both the operator V^eff and the response function necessary for evaluating polarisation. A detailed investigation of the lattice dynamics of an ideal crystal allowed the author to connect the parameters of the method with the dynamic matrix of an ideal crystal, i.e. eventually with its phonon spectra and eigenvectors, which can be found experimentally.