Parameter definitions for "debye"
It's probably useful to look first at the special features page. You may also want to look at one of the general help files, Sliders, or
Graphs.
Inputs
- SLIDERS
- force const B: Twice the force constant, in N/m, of the springs connecting nearest neighbors of the fcc structure. The unconventional factor of two in the force constant follows the definition in Ashcroft and Mermin, page 449, Problem 22.5. (Restricted to be positive.)
- v_s: The velocity of sound, in units of 10^6 cm/s, used in the Debye model. It is specified independently of the force constant, lattice constant and mass, and need not be consistent with them. (Restricted to be positive.)
- Tmax: Sets the maximum, in kelvin, of the temperature range displayed in the heat capacity and internal energy plots. The ten internal energy curves plotted are spaced in T at equal intervals, namely Tmax/10. (Restricted to values greater than 10.)
- lattice const: The lattice constant, in angstroms, of the fcc structure. (Restricted to be positive.)
- mass: The atomic mass, in units of 10^(-24) kg, of the atoms. (Restricted to be positive.)
- qx:, qy:, and qz: Define the Miller indices for the arbitrary direction in q-space along which the dispersion relations are plotted. (Restricted to integers.)
- MENUS
- compare with: allows comparison of the model calculation with experimental results both for the dispersion relations along any or all of the three symmetry directions, and for the heat capacities.
- nothing: No comparisons shown.
- lead: Experimental data for lead.
- copper: Data for copper.
- aluminum: Data for aluminum.
- show(left): The dispersion relations may be plotted in two different ways: either
- symmetry directions: along the symmetry directions (100), (110), and (111), as well as along the X-K line in reciprocal space; or
- arbitrary direction: along an arbitrary line in reciprocal space defined by the Miller indices (qx qy qz) which may be entered (as integers) in the sliders beneath the left-hand graph.
- show(right): Offers several choices for the plot in the right-hand graph:
- density of modes: The density of modes (or density of phonon states), in units of 10^9 modes/(rad/s)(cm^3) vs. angular frequency in units of 10^12 rad/s.
- heat capacity: The heat capacity, in J/K cm^3, vs. temperature in kelvin.
- internal energy: The internal energy spectral density, in J/[(rad/s)(cm^3)], vs. angular frequency in units of 10^12 rad/s.
- TOGGLES
- simulation: Turns on and off, in the right-hand graph, the display (in blue) of results from the simulation.
- Debye: Turns on and off, in the right-hand graph, the display (in red) of results from the Debye model.
- linear/log (above the right-hand graph) allows choice of linear or log-log plots in the right-hand graph. The log/log plot often appears erratic at the low end of the range. Ignore this range: "debye" is trying to deal with things like the log of zero.
- BUTTONS
- calculate: Initiates the calculation of the density of modes, the heat capacity, and the internal energy which are to be displayed in the right-hand graph. The key equivalent is the spacebar.
- double MC steps: Doubles the size of the data set used to construct the density of modes histogram, by calculating additional mode frequencies and adding to the existing results. The total accumulated number of q-samples is displayed as MC steps in the right hand graph. The key equivalent is the d-key: d for double.
- copy graph(left): See Graphs in the general help.
- copy graph(right): See Graphs in the general help.
- presets: Takes you to a tear-off menu with which you may select the presets. For more details, see the preset item in the miscellaneous help file.
- configure:
- number of MC points: Sets the number of points in q-space which are sampled by calculate to develop the density of modes. (Restricted to positive integer.)
- {revert: updates the listed configure parameters to the current values (which may have been changed by a preset command).}
- {close: Closes the configure window.}
- help: Opens the help system which you have already found!
- quit: Terminates "debye".
- ENTRY BOXES
- number of bins: The number of bins assigned to develop the histogram for the density of modes plot. Scales on density of modes and internal energy plots are likely to go haywire if number of bins is changed without also doing another calculate. (Restricted to positive integer.)
Outputs
- DISPLAYS
- left side: Displays the dispersion relations omega(q), with omega in rad/s and q in units of 1/angstroms, along either the symmetry directions in q-space, or else along an arbitrary direction specified by the Miller indices (qx qy qz) below the graph.
- right side: Displays the density of modes, heat capacity, or spectral density of the internal energy, as described for the right-hand show graph menu.
- READOUTS
- MC steps: Gives, in the corner of the right-hand graph, the accumulated number of q-points sampled to generate the histogram for the density of modes plot. This will change to RED if any parameter relevant to the calculation of the histogram, or if a preset, is changed. Only if MC steps is black can you rely on the right hand graph to show simulation results appropriate to the parameter values given on the panel. (The velocity for the Debye model, however, can be changed without raising the alarm, and the Debye model results will be updated automatically.)