Explanation of irregular trend in19F* (I=5/2) nuclear quadrupole interaction in CF4, SiF4, and GeF4

A theoretical investigation of the electric field gradient at excited nuclei¹⁹F^*(I=5/2) of the tetrafluorides CF₄, SiF₄, and GeF₄, has been carried out using the Self-Consistent Charge Extended Hückel procedure to obtain the electronic wave functions. The values of ¦e²qQ¦ that have been obtained are 50.3, 30.4, and 36.3 MHz for CF₄, SiF₄, and GeF₄, respectively, agreeing with the trend in recent experimental data. Physical reasons are presented for the trend, which is irregular as compared to expectations from Townes-Dailey Theory which would have predicted a continuus decrease in going from CF₄ to GeF₄.     

Probing the structure and energetics of dislocation cores in SiGe alloys through Monte Carlo simulations

We present a methodology for the investigation of dislocation energetics in segregated alloys based on Monte Carlo simulations which equilibrate the topology and composition of the dislocation core and its surroundings. An environment-dependent partitioning of the system total energy into atomic contributions allows us to link the atomistic picture to continuum elasticity theory. The method is applied to extract core energies and radii of 60 degrees glide dislocations in segregated SiGe alloys which are inaccessible by other methods.