.. _optimizer:

Optimizer
==============

The eon client provides three optimizers quick-min, conjugate gradients, and L-BFGS.

**[Optimizer]** parameters
--------------------------- 

**opt_method**: The optimization method to use.

    default: ``cg``

    options:

        ``box``: Optimizes the atom positions and box using quickmin

        ``cg``: Conjugate gradient

        ``qm``: Quickmin

        ``lbfgs``: Limited Memory Broyden-Fletcher-Goldfarb-Shanno QuasiNewton
        optimizer

        ``fire``: Fast inertial relaxation engine

**convergence_metric**: The metric to use to determine when an optimization is complete.

    default: ``norm``

    options:

        ``norm``: The norm of the entire force vector

        ``max_atom``: The maximum force on any non-frozen atom

        ``max_component``: The maximum force on any non-frozen degree of freedom

**converged_force**: When the **convergence_metric** is
smaller than this value (eV/A), the structure is considered minimized.

    default: ``0.01``

**max_move**: Maximum distance that an atom may be moved in a single
optimization step (Angstoms).

    default: ``0.2``

**time_step**: The dynamical timestep for the quickmin algorithm (fs).

    default: ``1.0``

**max_iterations**: The maximum number of optimization iterations that the will
be performed.

    default: ``1000``


L-BFGS
------

The L-BFGS implementation in Eon resets its memory if a move larger than the max_move is
attemped or if the angle between the force and the L-BFGS direction is larger than 90 degrees.


**lbfgs_memory**: The maximum number of previous gradients and positions that
are kept in memory for the L-BFGS algorithm.

    default: ``20``

**lbfgs_inverse_curvature**: The initial guess for inverse curvature at each step, which is used to
construct the inverse Hessian matrix. This setting is only used when **lbfgs_auto_scale** is ``False``.

    default: 0.01

**lbfgs_auto_scale**: The initial guess for the inverse hessian at each step is constructed by
estimating the curvature along the previous step direction. At the first step a forward finite difference
calculation along the force is used to estimate the curvature.

    default: ``True``