The Elastic Constants tab allows you to set parameters that define how the elastic constants will be calculated.
Number of steps for each strain: Specify the number of distorted structures generated for each strain pattern. An odd value implies that the undistorted structure will be among those generated. Even values are, therefore, recommended.
Maximum strain amplitude: Set the maximum distortion used. Values in excess of 0.01 are not recommended, since the crystal is likely to be beyond linear elasticity. However, values of 0.001 and below will generate a set of structures that are very similar to one another. In these circumstances, computational noise may become significant when comparing the calculated stress values for similar structures.
Use volume-conserving strains: When checked indicates that the strain patterns will be modified to use volume-conserving strains, when possible. This option should only be used if the standard set of strains is producing unsatisfactory results.
Strain pattern: Displays a matrix showing the nonzero components of the strain tensor for each generated strain. For example, the line:
1 0 0 1 0 0
means that the xx, yz (and zy) components of the strain tensor will be non-zero.
This matrix is not editable.
For trigonal symmetry, the orientation standard where C lies along the z-axis and A is in the xz plane must be used. For further details on the lattice orientation standard and how to set it, see the Viewing or changing the lattice parameters topic.
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Elastic constants theory
CASTEP Elastic Constants task
CASTEP Elastic Constants dialog
Options tab - CASTEP Elastic Constants dialog