Parameter definitions for "burgers"
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
- alpha: compressive force constant, in units of Vo/a^2, of the nearest neighbor interaction for atoms in the blue plane. Vo is a scale parameter defining the strength of the interactions across the slip plane between red and blue atoms, and a is the lattice constant of the red plane. (Restricted to positive values.)
- beta: shear force constant, in units of Vo/a^2, of the nearest neighbor interaction for atoms in the blue plane.
- c/a ratio: ratio of the equilibrium lattice constant for the blue plane (c) to that for the red plane (a). (Restricted to positive values.)
- impurity size: the impurity atom is coupled to its neighbors with the same force constants as the blue atoms, but with an equilibrium nearest neighbor distance for a lattice of impurities which is impurity size times the lattice constant a of the red plane. (That is, the equilibrium radius of an impurity atom is impurity size times a/2.)
- speed: The number of computational steps between successive animation displays. (Restricted to positive integers.)
- x shear stress: shear stress, in units of Vo/a^3, applied across the red/blue slip plane. Positive values correspond to a force to the right on the blue plane, to the left on the red. (Note: after a new preset is chosen, this slider returns to its standard default value as soon as the coarse/fine toggle is clicked.)
- MENUS
- resolution:adjusts the sensitivity of the shear stress slider.
- coarse: sets the full range of the slider, usually, to -1 to +1 Vo/a^3, where Vo is a scale parameter defining the strength of the interactions across the slip plane between red and blue atoms, and a is the lattice constant of the red plane.
- fine: reduces the full range of the shear stress slider by about a factor of ten.
- TOGGLES
- run/stop starts and stops the calculation and animated display. The key equivalent is the space-bar.
- BUTTONS
- remove dislocations: returns the atomic configuration of the blue plane to the undislocated square lattice of lattice constant c. Impurities and vacancies are NOT destroyed. Key equivalent is the i-key.
- 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:
- lattice width: changes the number of blue atoms in a row. (Restricted to positive integers.)
- lattice height: changes the number of blue atoms in a column.(Restricted to positive integers.)
- stepsize fraction: adjusts the stepsize in the algorithm. A larger value speeds the calculation, a smaller value improves stability. (Restricted to positive values.)
- {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 "burgers"
Outputs
- DISPLAYS
- animation display: red atoms are the top-most plane of atoms of the half-crystal below a slip plane. In "burgers" they are fixed and do not move. Blue atoms are the bottom-most plane of atoms of the half-crystal above the slip plane. Blue atoms are coupled to each other harmonically with the force constants alpha and beta. Blue atoms move in an attractive egg-carton potential V(x,y) = -(Vo/2 pi){cos(2 pi x/a) + cos(2 pi y/a)}, with minima at the positions over the red atoms.
- READOUTS
- <delta x> gives the average x-component of the displacements of the atoms in the blue plane in the latest calculational step. It is useful as a monitor to verify whether the animation has settled to an equilibrium array or is still evolving.