The detailed electronic structures and geometries of Si(100) reconstructed surfaces are investigated by a self-consistent calculation with a norm-conserving nonlocal pseudopotential. We concentrate on the dimer model and on (2

A technique based on the path-integral effective-potential theory to calculate the thermodynamic properties of a linear chain of atoms is extended to include all-neighbor interactions. The configuration averages are performed using the classical Monte Carlo technique. The theory is applied to a system interacting with a Mie-Lennard-Jones potential to make contact with earlier work. Results for the internal energy and specific heat are presented and compared with those using only nearest-neighbor interactions and the quantum Monte Carlo method. This is a useful step toward the application of the effective-potential theory to realistic systems with long-range interactions.

We demonstrate that the propagation of a light wave in an elliptic gradient-index medium can be regarded as a joint fractional Fourier transform. The distinctive features of the Wigner distributon function and the recurrence of the original function are analyzed qualitatively. q1998 Elsevier Science B.V. All rights reserved.

In this paper the Laguerre-Gaussian (LG) series representation of the twodimensional fractional Fourier transform is derived from conventional ordinary Fourier transform in polar coordinates. The kernel of this series representation is constituted by Laguerre-Gaussian functions, from which the series representation of a fractional Hankel transform can be easily derived. The connection between the gradient-index medium and the LG series representation is illustrated as an example of its applications.

We present a theoretical study of the valence-band offsets (VBOs) of the pseudomorphic Si1-x-yGexCy/Si(001) heterojunctions. Our calculation is based on the ab initio pseudopotential method, the virtual-crystal approximation, and the average-bond-energy theory. It is found that the VBO is sensitive to the strain condition. Initial addition of carbon increases the VBO of the relaxed Si12x2yGexCy/Si(001) heterostructures. For constant Ge fraction, the VBO decreases and increases with increasing the C fraction in the case of the compressive and tensile strains, respectively. The trends of our results are in agreement with those of other theoretical and experimental results.