.. _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 `_ .. [#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 `_ .. [#kastner08_014106] J. Kästner and P. Sherwood, "Superlinearly converging dimer method for transition state search," *J. Chem. Phys.* **128**, 014106 (2008) `DOI `_