Tight-binding calculations of the band structure and total energies of the various polytypes of silicon carbide

We present electronic structure and total energy calculations for SiC in a variety of polytype structures using the NRL nonorthogonal tight-binding method. We develop one set of parameters optimized for a combination of electronic and energetic properties using a sp basis, and one optimized for electronic properties using a spd basis. We compute the energies of polytypes with up to 62 atoms per unit cell, and find that the hexagonal wurtzite structure is highest in energy, the 4H structure is lowest in energy, and the cubic zinc-blende structure is in between, in agreement with our linear augmented plane-wave and other calculations. For the spmodel we find that the electronic structure of the cubic and hexagonal structures are in good agreement with densityfunctional theory calculations only for the occupied bands. The spd parametrization optimized for the electronic structure of the zinc-blende and wurtzite structures at the equilibrium volume reproduces nearly perfectly both the valence and conduction bands. The sp tight-binding model also yields elastic constants, phonon frequencies, stacking fault energies, and vacancy formation energies for the cubic structure in good agreement with available experimental and theoretical calculations. Using molecular dynamics simulations we compute the finite-temperature thermal expansion coefficient and atomic mean-square displacements in good agreement with available first-principles calculations.