A quantum field theory of lattice dynamics and melting in nonprimitive crystals

A unified theory of lattice dynamics and melting is presented from the view-point of quantum field theory at finite temperature. The lattice dynamics and the melting in nonprimitive crystals which contain more than one atom in a unit cell are investigated in the random phase approximation using the two-bands model for atoms. The gap equation for atoms plays an essential role in constructing the lattice dynamics and determining the melting temperature. Our theory is applied to sphalerite and diamond structure in the nearest-neighbour approximation for the interatomic potentials. Our theory covers all types of crystals.