4.7 Force calculation and structure relaxation
To calculate forces that the atoms experience, one needs to add a few more parameters in the INPUT file. Below is an example for the Si dimer.
suffix Si2_dimer
calculation relax
gamma_only 1
nstep 100
force_thr_ev 0.01
move_method cg
out_stru 1
trust_radius_ini 0.5
• nstep the number of ionic iteration steps.
• force_thr_ev the threshold for the force, below which the geometry relaxation is considered to be converged. The unit is eV/Angstrom.
• move_method the algorithm used for geometry optimization. Possible choices are:
– cg : Conjugate Gradient (CG) algorithm
– bfgs : BroydenFletcherGoldfarbShanno (BFGS) algorithm
– sd : Steepest descend algorithm
The CG method is recommended.
• out_stru output the structure of each step or not.
• trust_radius_ini the initial radius of the relaxation. We advise you not to change this parameter, unless you are sure that the initial structure is close to the final structure.
