steplength is the initial step length in the scaled parameter space (default 0.3). In the AH-method this is dynamically adjusted, and can have a maximum value ahmax (see TRUST).
drmax is the initial max change of distances (in bohr, default 0.3). In the AH-method this is dynamically adjusted up to a maximum value of drmax1 (default 0.5 bohr).
damax is the initial max change of angles (in degree, default 2). In the AH-method this is dynamically adjusted up to a maximum value of damax1 (default 10 degrees).