.. _hyperdynamics: 

=============
Hyperdynamics
=============

The hyperdynamics method uses a bias potential which should be zero at
transition states and positive in minima in order to accelerate the rate of
transitions. [#voter97_3908]_ The hyperdynamics time step :math:`\delta t`
can be obtained from the molecular dynamics simulation time step :math:`\delta
t^b` multiplied by a boost factor :math:`e^{\beta \Delta V}`, where
:math:`{\Delta V}` is the bias potential.

There are several possible forms of bias potential. In EON, we have implemented
the bond-boost method, [#miron03_6210]_ where the bias potential is controlled
by the maximal (fractional) change in any bond length in the system.  This is a
good bias potential for systems in which the dynamics is governed by bond
breaking and forming events.

You can run a hyperdynamics job by setting the **bias_potential** option.
It may be run with the ``dynamics`` or ``parallel_replica`` job.

[Hyperdynamics] Options
=======================

**bias_potential**: 

    default: ``none``

    options:

        ``bond_boost``: bond boost method

        ``none``: with no bias potential, run regular MD

**bb_dvmax**: 

    default: ``0.0``

    The magnitude of the bond-boost bias potential.

**bb_rmd_time**: 

    default: ``100.0``

    Regular MD duration used to determine the equilibrium bond length before the bias potential is added.

**bb_rcut**: 

    default: ``3.0``

    All bonds which belong to the tagged atoms and are shorter than a cutoff of rcut will be included in the bond-boost potential.

**bb_stretch_threshold**: 

    default: ``0.2``

    Defines the bond-boost dividing surface. It should be smaller than the
    maximum fractional nearest-neighbor bond stretch or compression at any
    transition state.

**bb_ds_curvature**: 

    default: ``0.95``

    The curvature near the bond-boost dividing surface, it should has a value
    <= 1. We recommend the value to be 0.9-0.98.

.. rubric:: References

.. [#voter97_3908] A.F. Voter "Hyperdynamics: Accelerated Molecular Dynamics of Infrequent Events" *Phys. Rev. Lett.* **78**, 3908 (1997)

.. [#miron03_6210]  R.A. Miron and K.A. Fichthorn "Accelerated molecular-dynamics of rare events with the bond-boost method" *J. Chem. Phys.* **119**, 6210 (2003)

