Conformer Search (GOAT)#

For flexible molecules, it is important to identify the low energy conformational space to provide the most accurate model of the investigated system. The global optimizer algorithm (GOAT) within ORCA can help to automatically find the global minimum structure and the ensemble around it. GOAT can be envoked by the simple input keyword GOAT:

!GOAT XTB

*XYZFILE 0 1 inp.xyz

Note

As a GOAT run involves a large number of geometry optimizations, it is recommended to parallelize the calculation, e.g. via the PAL4 keyword. Further, specifically for large systems, the usage of fast semi-empirical methods like GFN2-xTB speeds up the calculation. Nevertheless, GOAT can be used with any method in ORCA that is capable of optimizing geometries.

Example: Diclofenac#

As an example, we will use to find the global minimum conformation of Diclofenac starting from the PubChem structure.

../_images/diclofenac.png — Figure: Diclofenac#

The input looks like:

!GOAT XTB

*XYZFILE 0 1 diclofenac.xyz

After the successful GOAT run, the global minimum structure is stored in the basename.globalminimum.xyz file and the full structure ensemble in the basename.finalensemble.xyz file. In this case, GOAT found 17 unique conformers. The corresponding energies and weights are reported in the output file:

                     ------------------------------
                                           _
                                          | |
                          __ _  ___   __ _| |_
                         / _` |/ _ \ / _` | __|
                        | (_| | (_) | (_| | |_
                         \__, |\___/ \__,_|\__|
                         __/ |
                        |___/

                      A Global Optimizer Algorithm
                     ------------------------------
[...]
                Global minimum found!
                Writing structure to diclofenac.globalminimum.xyz

                # Final ensemble info #
                Conformer     Energy     Degen.   % total   % cumul.
                              (kcal/mol)
                ------------------------------------------------------
                        0     0.000          1      75.54      75.54
                        1     0.976          1      14.56      90.10
                        2     1.991          1       2.62      92.72
                        3     2.028          1       2.46      95.18
                        4     2.413          1       1.29      96.47
                        5     2.572          1       0.98      97.45
                        6     2.621          1       0.91      98.36
                        7     2.799          1       0.67      99.03
                        8     3.339          1       0.27      99.30
                        9     3.420          1       0.24      99.53
                       10     3.781          1       0.13      99.66
                       11     3.827          1       0.12      99.78
                       12     4.027          1       0.08      99.86
                       13     4.373          1       0.05      99.91
                       14     4.614          1       0.03      99.94
                       15     4.624          1       0.03      99.97
                       16     4.752          1       0.02     100.00
                       17     5.951          1       0.00     100.00

                Conformers below 3 kcal/mol: 8
                Lowest energy conformer    : -55.771201 Eh
                Sconf at 298.15 K          :  1.83 cal/(molK)
                Gconf at 298.15 K          : -0.17 kcal/mol

                Writing final ensemble to diclofenac.finalensemble.xyz

We see, that the conformer space of Diclofenac is dominated by the two conformers 1 and 2, with their weights summing up to 90.1 %. The 10 lowest conformers look like:

Conformer Search (GOAT)#

Example: Diclofenac#

Structures#