We investigate the band-gap modiication by collapsing deformation in C, BN, and BC3 nanotubes through rst-principles pseudopotential calculations. Semiconductor-metal transitions occur when zigzag C and armchair BC3 nanotubes undergo collapsing deformation, while in zigzag BN tubes, a variation of band gaps from 5 to 2 eV is found. On the other hand, the band gaps of armchair BN and zigzag BC3 ...

A model is tested to rapidly evaluate the vibrational properties of alloys with site disorder. It is shown that length-dependent transferable force constants exist and can be used to accurately predict the vibrational entropy of substitutionally ordered and disordered structures in Au-Cu, Au-Pd, and Cu-Pd. For each relevant force constant, a length-dependent function is determined and fitted to...

An analytical theory of intervalley mixing at semiconductor heterojunctions is presented. Burt’s envelope-function representation is used to analyze a pseudopotential Hamiltonian, yielding a simple d-function mixing between G and X electrons and light and heavy holes. This coupling exists even for media differing only by a constant band offset (i.e., with no difference in Bloch functions). [S00...