1 Numerical dispersion curves for copper

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"debye" calculates the dispersion curves for an fcc structure in terms of the lattice constant, the atomic mass, and a single force parameter B defined in Ashcroft and Mermin (page 449, problem #5). In this preset the atomic mass and lattice constant are set as appropriate to copper, and B to an arbitrary value of 25 N/m.

The graph on the left displays the dispersion curve for q-values along the (1 0 0) direction in reciprocal space. Enter other directions, e.g., (1 1 0), using the sliders under the graph. Why are there three branches in the (1 1 0) direction but only two along (1 0 0)? Try some other directions.

Select symmetry directions from the menu above the graph to see a summary of the dispersion relations along all three symmetry directions, as well as along a line (X -> K) in the square face of the Brillouin Zone (BZ).

Select copper from the compare with menu to display neutron diffraction data for copper. Can you improve the fit by adjusting B with the slider?