Geometry Optimisation

Introduction

The standard geometry optimiser for ChemShell is the DL-FIND optimisation library.

• DL-FIND is a flexible optimiser featuring local and global minimisation, transition state search and conical intersection optimisation algorithms. Transition state methods include P-RFO, dimer and nudged elastic band. Cartesian and redundant internal coordinates (including HDLCs) are supported.

Examples of how to use DL-FIND are provided in the tutorial.

A number of alternative optimisation modules are also available in ChemShell. These are no longer under development and have largely been superseded by DL-FIND. However they may still be of interest for features that DL-FIND does not currently support, such as Z-matrix optimisation.

• Newopt This is a general purpose optimiser with a modular (and extensible) design. Tcl scripts can be used to define the optimisation algorithms, and new target functions can be interfaced. The code includes two target functions for molecular geometry optimisation, zopt for mixed cartesian/z-matrix and copt for pure cartesian coordinates.
• Opt This is the GAMESS-UK geometry optimiser, which will optimise in Z-matrix internal coordinates. Saddle point searches using the eigenvector following and Jorgensen-Simons approaches are possible.
• HDLCOpt This optimiser, based on redundant internal coordinates as suggested by Baker, was developed as part of the QUASI project. HDLCOpt is a deprecated module and will be removed in future versions of ChemShell. DL-FIND should be used instead.