Specifying an initial strain

You may optionally specify an initial deformation tensor using the format...

begin deformation
0.00 0.00 0.02
0.00 0.00 0.00
0.00 0.00 0.00
end deformation

This is the deformation tensor applied to your structure. It is defined by the following equation:

where are the deformed lattice vectors, and are the lattice vectors specified in your input file. This can be an easy way to apply a shear strain to a cubic crystal, for instance.

There are times when it is useful to ensure that a given direction is held fixed during the relaxation process. This does not involve a constraint on the relaxation, as there are three rotational degrees of freedom. One can also arrange to maintain fixed a plane which contains the fixed direction.

To keep the fixed, and also keep the zx plane from rotating, you could specify...

mugwump_vector     0 0 1
desideratum_vector 1 0 0