The Normal Modes of Vibration of a Body-Centered Cubic Lattice

An atomic model is set up for the purpose of finding the normal modes of vibration of a body-centered cubic lattice. A method is presented for selecting suitable atomic force constants from the macroscopic elastic properties of tungsten, which satisfy the isotropy condition but not the Cauchy relation. Actual solutions of the secular equation are then carried out under the assumption that each atom is affected by only its fourteen nearest neighbors. Numerical computations yield a frequency distribution characterized by two steep maxima. This is used in evaluating the specific heat and the intensity of reflection of x-rays as functions of temperature, and the results are compared with the Debye theory.