Optimize Geometry

[Inaoton]

Hello
                    During Optimization  which parameter does the maximum step length accounts for? (default=0.2 Angstom)
  e.g. if i want to optimize a crystal structure with lattice parameters 'a' and 'c' , does the optimizer varies both parameters 'a' and 'c' or only one of             them?

[Petr Khomyakov]

1. This is the maximum step length the geometry optimizer may take. If you have a problem converging to equilibrium geometry during optimization, you may want to reduce the maximum step length.

2. You may optimize all the lattice parameters simultaneously, or any pair of them, or a particular one, or none of them, depending on how you set constraints in the geometry optimization settings (Constrain Lattice Vectors). The fault is not to optimize any of the lattice parameters, i.e., to do ion relaxation only.

[Jess Wellendorff]

The ATK Manual gives this sort of information and much more: http://docs.quantumwise.com/manuals/Types/OptimizeGeometry/OptimizeGeometry.html