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Force calculation and structure relaxation

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To calculate the atomic forces for a given structure without ion relaxation, set ‘calculation’ to ‘scf’, set input parameter ‘force’ to 1.

calculation scf
force 1

To relax the atom position without change cell shape, one needs to add a few more parameters in the INPUT file. Here is an example for the Si dimer. In this case, the forces are calculated by default.

calculation relax
gamma_only 1
nstep 100
force_thr_ev 0.01
move_method cg
out_stru 1
trust_radius_ini 0.5

  • calculation relax

    relax atom positions with fixed lattice vectors.

  • nstep

    the maximal 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

    Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm

  • cg_bfgs

    A mixed cg-bfgs method. For detail description, check out the variable cg_threshold in the list of input keywords.

  • 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.

An example for structure relaxation calculation can be found at tests/108_PW_RE.

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