
.. _dimer:

=====
Dimer
=====

The dimer method of Henkelman and Jónsson with improvements by Heyden et al
and Kästner and Sherwood for estimating the lowest eigenmode using only first derivatives.
[#henkelman99_7010]_ [#heyden05_224101]_ [#kastner08_014106]_

The dimer separation is set in the **[Main]** section with the finiteDifference parameter.

[Dimer] Options
===============

**opt_method**: Optimization algorithm to choose the dimer rotation direction

    default: ``cg``

    options:

        ``sd``: steepest descent, rotate along the rotational force.

        ``cg``: conjugate gradient, rotate along conjugate directions.

        ``lbfgs``: Limited memory Broyden-Fletcher-Goldfarb-Shanno Quasi-Newton optimizer.

**converged_angle**: The dimer is considered converged if it will be rotated
fewer degrees than this angle.

    default: ``5.0``

**rotations_max**: This is the maximum number of rotations allowed for the
dimer for each minimum mode estimation.

    default: ``10``


.. rubric:: References

.. [#henkelman99_7010] G. Henkelman and H. Jónsson, "A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives," *J. Chem. Phys.* **111**, 7010-7022 (1999). `DOI <http://dx.doi.org/10.1063/1.480097>`_

.. [#heyden05_224101] A. Heyden, A.T. Bell, and F.J. Keil, "Efficient methods for finding transition states in chemical reactions: Comparison of improved dimer method and partitioned rational function optimization method," *J. Chem. Phys.* **123**, 224101 (2005). `DOI <http://dx.doi.org/10.1063/1.2104507>`_

.. [#kastner08_014106] J. Kästner and P. Sherwood, "Superlinearly converging dimer method for transition state search," *J. Chem. Phys.* **128**, 014106 (2008) `DOI <http://dx.doi.org/10.1063/1.2815812>`_
