Mod:Hunt Research Group/orca6 GOAT
Contents
Using GOAT for Global Minimum/Conformer Search
GOAT (Global Optimisation Approximation) is a tool that engages in minima hopping to attempt to find the global minimum energy for a given atomic structure. In the process it produces a wide-ranging conformer search, which is returned as output. It can function as an alternative to CREST for conformer searches, and is run as a typical ORCA file.
Setting up a GOAT run
Input files for GOAT follow the standard rules for Orca input, but require the addition of the GOAT keyword to the input (i.e. "![...] GOAT"). You must also specify a calculation method. GOAT supports any method that Orca uses (so you can run a conformer search using DFT or HF if you so choose), but generally it is fastest to use XTB (this is the method used by CREST). DFT GOAT runs may take a long time -- be careful with your usage if you are choosing to run it with a higher-level methodology!
Tip: make sure you have a specific directory set aside for GOAT, as it will dump a lot of files (in a similar manner to CREST) that will otherwise clog up your working directory.
Parameter alterations
Initial use on some copper-amino acid complexes found issues with GOAT returning identical conformers as distinct ones. In order to avoid this, you may wish to increase the RMSD parameter, which by default is set at 0.125. This can be done by adding the %GOAT block as follows below the main input line:
!.... %GOAT RMSD <float> END
Analysing the GOAT output
GOAT will output several files in the same manner as CREST. Of most interest are \<inputfilename\>.finalensemble.xyz, \<inputfilename\>.globalminimum.xyz, and \<inputfilename\>.out.
.out file
The .out file will show whether the job has terminated normally. If you scroll up from the bottom of a nominally-terminated file, you will find a list of all the conformers that it has found. These are ordered from lowest to highest energy, with relative energy presented in kCal/mol in the second column. GOAT also computes the proportion of these conformers in a sample based on their energies, which is listed in the second-from-right column.
.finalensemble.xyz file
This file contains all the xyz structures for the found conformers, in the same order as those in the .out file. It can be opened in a visualiser e.g. JMOL to visually assess the conformers. To extract specific conformer xyz files and transform them to com files you can use the script here !INSERT SCRIPT LINK!
globalminimum.xyz
This file contains only the posited global energy minimum structure, i.e. the first structure listed in the .out file.
