Controlling the relaxation process

If job relax or job relax_from_checkpoint or job relax_recycle_H is chosen, the variable relax_what allows different ways to relax a structure:

relax_what force

or

relax_what stress

or

relax_what force_and_stress

Default: relax_what force_and_stress

Another variable allows to manipulate the way the relaxation is done:

Set

relax_how gradient

to simply follow along the forces and stress, without updating the inverse of the Hessian matrix.

Default: update the Hessian

With the variable relax_how the line-minimization can be altered also:

relax_how slow        # do 3 steps per line minimization always
relax_how normal      # do up to 3 steps, but only if necessary
relax_how fast        # dont do line minimization at all

Default: relax_how normal

Note: This can be combined with the gradient option with a statement like relax_how normal_gradient

The parameter lambda_limit allows you to limit the size of relaxation steps to a certain number. Normally, lambda should be on the order of 1. Sometimes, especially in the beginning of the iteration, and if the H matrix is initialized to small, lambda can become to big, and the algorithm bombs out. It is then advisable to limit lambda with a line like that:

lambda_limit 4.0

Default: lambda_limit 1e6 (no limit)

The statement starting_distortion followed by nine floating point numbers allows to set an initial distortion of the lattice. This feature is only for debugging, and not recommended for use.