6.4. GOAT: global geometry optimization and ensemble generator¶
If instead of trying to optimize a single structure, starting from a given guess geometry, you want to find the global minimum or the ensemble around it, ORCA features a Global Optimizer Algorithm (GOAT) inspired by Wales and Doye’s basin-hopping [877], Goedecker’s minima hopping [306], Simulated Annealing and Taboo Search.
The idea is to start from somewhere on the potential energy surface (PES; red ball on Fig. 6.24), go first to the nearest local minimum (blue ball), and from there start pushing “uphill” on a random direction until a barrier is crossed. Then a new minimum is found and the process is restarted, with another uphill push followed by an optimization. After several of these GOAT iterations (uphill + downhill), if no new global minimum was found between the two last global iterations.
Fig. 6.24 A simple depiction of the difference between a regular geometry optimization (above), and the GOAT global optimizer (below). By using the latter, one finds not only one local minimum but the global one and the conformational ensemble around it.¶
Since structures are collected along the way to the global minimum, we have in the end not only the global minimum, but also the conformational ensemble for that molecule, meaning all the conformations it can have and their relative energies. This is also useful later to compute Boltzmann-averaged spectra and properties.
The idea is similar to what is done with CREST from the group of Prof. Grimme [697], except that no metadynamics is required and thus much less gradient runs are needed. It is thus suitable not only for super fast methods such as XTB and force-fields, but can also be used directly using DFT or with any method available in ORCA.
Please note that there is no ab initio way to find global minima for arbitrary unknown functions, and stochastic methods are the most efficient on finding these. The drawback is that it is based on random choices, so that many geometry optimizations are needed - here in the order of \(100\times\) the number of atoms. Good news is: these can be efficiently parallelized (even multinode) and this number can be brought down to less than \(3\times\) the number of atoms (see below)!
6.4.1. GOAT simple usage example - Histidine¶
Let’s start with a simple example, the amino acid histidine:
Fig. 6.25 A histidine molecule.¶
By simply looking at its Lewis structure, it is not at all evident that there are actually at least 20 conformers in the 3 kcal/mol range from the global minimum on the XTB PES! In order to find them, one can run:
!XTB GOAT #XTB version 6.4.0
* xyz 0 1
N -0.13033 -0.28496 -0.67901
C 1.30551 -0.36383 -0.41824
C 1.51611 -1.04435 0.94169
O 0.58926 -1.43597 1.64771
C 1.97932 1.02323 -0.44331
H 2.41593 1.27074 0.53237
H 1.24598 1.81337 -0.65132
C 3.04894 1.09545 -1.48009
N 2.77779 1.01389 -2.82650
C 3.97051 1.07618 -3.48654
H 4.04071 1.01588 -4.56429
N 4.97724 1.21154 -2.65295
C 4.41545 1.24248 -1.40412
H 5.02774 1.35929 -0.51882
H 1.85722 0.88822 -3.24287
H -0.75420 -0.54264 0.08211
H 1.72153 -1.03742 -1.17913
H -0.47113 0.20468 -1.50142
O 2.79298 -1.20515 1.35271
H 3.59528 -0.86615 0.74156
*
The command to call the global optimizer is simply !GOAT, like you would
with !OPT, and its options can be given under the %GOAT block as usual.
You can give it together with any other method available in ORCA, but it
needs to be a fast one because a lot of geometry optimizations need to
be done. Here we will just use GFN2 (or !XTB). What will happen next is:
First a regular geometry optimization will be done to find the minimum closest to the input structure.
With that information in hand, the number of necessary GOAT iterations will be computed and divided among
NWorkers(8 by default).Each
Workerhas its own parameters and will run a certain number of geometry optimizations.After all workers in a global cycle are done, data will be collected and a new cycle will begin. There will be at least a “Minimum global steps” number of global cycles like this.
Once the difference between two global steps is negligible, it stops, collects everything and prints the ensemble energies and a file with all structures.
6.4.2. Understanding the output¶
After the usual geometry optimization, the output looks like:
Global parameters
-----------------
GOAT version ... default
Minimum global steps ... 3
Number of base workers ... 4
Split workers by ... 2
Final number of workers ... 8
Number of available CPUs ... 16
Parameter list (worker : temperature) ... 0 : 2903.97, 1 : 1451.98,
2 : 725.99, 3 : 363.00,
4 : 2903.97, 5 : 1451.98,
6 : 725.99, 7 : 363.00
GradComp (mean : sigma) ... 1.00 : 0.50
Number of atoms ... 20
Number of fragments ... 1
Flexibility parameter ... 0.45
Optimizations per global step ... 160
Optimizations per worker ... 20
Filtering criteria
------------------
RMSD ... 0.125 Angs (atom. pos.)
EnDiff ... 0.100 kcal/mol
RotConst ... 1.00-2.50 %
Maximum Conf. Energy ... 6.000 kcal/mol
Thermodynamics
--------------
Ensemble temperature ... 298.15 K
Degeneracy of conformers ... 1
*No rotamers will be included in Gconf
On the top there is some general information. Most important here is
that we have 8 workers and 1 CPU, meaning each worker will run only
after the other is done. If you want to speed up, just add more CPUs via
e.g., !PAL8 and workers will run in parallel making it 8x faster. GOAT
can also run multinode, so feel free to use any number of processors via
%PAL. In the end the filtering criteria used to differentiate conformers
and rotamers is printed.
The default filtering is precisely the same as that of CREST: RMSD of
atomic positions together with the rotational constant, considering its
anisotropy. For GOAT-EXPLORE (see below), the default RMSD metric is
based on the eigenvalues of the distance matrix instead, since it is
invariant to translations, rotations and the atom ordering, which
changes quite often in these cases.
After that, the algorithm starts:
------------------------------------------------------------------------------
Iter MinTemp MaxEn GradComp NOpt NProcs Output
------------------------------------------------------------------------------
0 2903.97 60.00 1.00 : 0.50 20 2 HIS.goat.0.0.out
1 1451.98 60.00 1.00 : 0.50 20 2 HIS.goat.0.1.out
2 725.99 60.00 1.00 : 0.50 20 2 HIS.goat.0.2.out
3 363.00 60.00 1.00 : 0.50 20 2 HIS.goat.0.3.out
4 2903.97 60.00 1.00 : 0.50 20 2 HIS.goat.0.4.out
5 1451.98 60.00 1.00 : 0.50 20 2 HIS.goat.0.5.out
6 725.99 60.00 1.00 : 0.50 20 2 HIS.goat.0.6.out
7 363.00 60.00 1.00 : 0.50 20 2 HIS.goat.0.7.out
GOAT Global Iter 1
Iter Min En Sconf Gconf
Hartree cal/(molK) kcal/mol
=========================================
1 -34.346656 4.432 -0.551
0 2903.97 60.00 1.00 : 0.50 20 2 HIS.goat.0.0.out
1 1451.98 60.00 1.00 : 0.50 20 2 HIS.goat.0.1.out
2 725.99 60.00 1.00 : 0.50 20 2 HIS.goat.0.2.out
3 363.00 60.00 1.00 : 0.50 20 2 HIS.goat.0.3.out
4 2903.97 60.00 1.00 : 0.50 20 2 HIS.goat.0.4.out
5 1451.98 60.00 1.00 : 0.50 20 2 HIS.goat.0.5.out
6 725.99 60.00 1.00 : 0.50 20 2 HIS.goat.0.6.out
7 363.00 60.00 1.00 : 0.50 20 2 HIS.goat.0.7.out
GOAT Global Iter 2
Iter Min En Sconf Gconf
Hartree cal/(molK) kcal/mol
=========================================
1 -34.346656 4.432 -0.551
2 -34.346656 4.528 -0.559
0 2903.97 60.00 1.00 : 0.50 20 2 HIS.goat.0.0.out
1 1451.98 60.00 1.00 : 0.50 20 2 HIS.goat.0.1.out
2 725.99 60.00 1.00 : 0.50 20 2 HIS.goat.0.2.out
3 363.00 60.00 1.00 : 0.50 20 2 HIS.goat.0.3.out
4 2903.97 60.00 1.00 : 0.50 20 2 HIS.goat.0.4.out
5 1451.98 60.00 1.00 : 0.50 20 2 HIS.goat.0.5.out
6 725.99 60.00 1.00 : 0.50 20 2 HIS.goat.0.6.out
7 363.00 60.00 1.00 : 0.50 20 2 HIS.goat.0.7.out
GOAT Global Iter 3
Iter Min En Sconf Gconf
Hartree cal/(molK) kcal/mol
=========================================
1 -34.346656 4.432 -0.551
2 -34.346656 4.528 -0.559
3 -34.346656 4.541 -0.560
Global minimum found!
Writing structure to HIS.globalminimum.xyz
On the top header one can see what are the temperatures used, the maximum energy allowed during an uphill step, the maximum coefficient for gradient reflection, the number of optimizations done per worker, the number of processors used for each and the local output file name.
The names of the output files are chosen as
BaseName.goat.globaliteration.workernumber.out. These are deleted after
the run by default, but can be kept by setting KEEPWORKERDATA TRUE under
%GOAT.
During each global iteration, the minimum energy so far, the conformational entropy \(S_{\rm conf}\) and the conformational Gibbs free energy \(G_{\rm conf}\) are printed. Since there are no rotamers here, the entropy is calculated only on the basis of the conformer energies and its convergence hints to the completeness of the ensemble created.
6.4.3. The final ensemble¶
In this case, as you can see, it already found the global minimum after the first global cycle with E = -34.346656 Hartree, but it keeps running for at least 3 cycles, following the defaults. This happens because it is a small molecule, but it is not necessarily so and more cycles will be done if needed.
The final relative energies of the ensemble are printed afterwards,
together with a BaseName.finalensemble.xyz file:
# Final ensemble info #
Conformer Energy Degen. % total % cumul.
(kcal/mol)
------------------------------------------------------
0 0.000 1 37.96 37.96
1 0.503 1 16.25 54.20
2 0.914 1 8.11 62.32
3 1.159 1 5.37 67.68
4 1.297 1 4.25 71.94
5 1.320 1 4.09 76.03
(...)
41 5.180 1 0.01 99.98
42 5.199 1 0.01 99.99
43 5.491 1 0.00 99.99
44 5.547 1 0.00 99.99
45 5.861 1 0.00 100.00
Conformers below 3 kcal/mol: 22
Lowest energy conformer : -34.346656 Eh
Sconf at 298.15 K : 4.54 cal/(molK)
Gconf at 298.15 K : -0.56 kcal/mol
Writing final ensemble to HIS.finalensemble.xyz
Just for the record, here is how the four lowest lying conformers look like:
Fig. 6.26 The four lowest conformers found for histidine on the XTB PES.¶
Whenever using GOAT, the EnforceStrictConvergence policy from ORCA’s optimizer
is set to TRUE. This is recommended here the ensure equal criteria for
different molecules in the ensemble. It can be turned off by setting
%GEOM EnforceStrictConvergence FALSE END.
The regular optimization thresholds are already good, but it might also
be a good idea to use !TIGHTOPT to make sure all your ensemble molecules
are well converged, specially for the GOAT-EXPLORE!
6.4.4. GOAT-ENTROPY: expanding ensemble completeness by maximizing entropy¶
If you want to be as complete as possible in terms of the ensemble, you
can use the !GOAT-ENTROPY keyword instead. This will not only try to
find the global minimum until the energy is converged, but will actually
only stop when the \(\Delta S_{\rm conf}\) also converges to less than 0.1
cal/(molK), which is equivalent to maximizing the conformational
entropy (the threshold can be altered – see keyword list below).
This will push the algorithm so that all conformers around the global minimum should be found together with it. Both temperature and \(\Delta S_{\rm conf}\) can be changed via specific keywords shown at the list below. A higher temperature will make the \(\Delta S_{\rm conf}\) more sensitive to changes in high energy conformational regions and should make the search even more complete.
Being more explicit, the conformational entropy, enthalpy and Gibbs free energy are calculated according to:
where \(\beta = \frac{1}{k_BT}\) and \(g_i\) is the “degeneracy” of conformer \(i\), i.e. its number of rotamers. This is the correct approach to deal with degenerate states [699]. The only difference from the reference above is that \(g'_i\) is always one and we don’t discriminate any factor for “geometrical enantiomers”.
6.4.5. More on the \(\Delta S_{\rm conf}\)¶
It is important to say that, by default, the \(\Delta S_{\rm conf}\) is not the same as that found by a default CREST run. There it includes also the rotamer degeneracy on the calculation of the entropy, while here that is 1. The reasons for that are:
There are formal arguments for using only one, assuming that rotamers are indistinguishable. Please check Grimme’s reference [699] for details.
For systems with many rotamers, e.g. molecules with 3 tert-butyl groups which give rise to at least (\(27^3\)) 19683 rotamers per conformer, the algorithm will never find all of these anyway.
When calling
GOAT-ENTROPY, it is the entropy of the conformers that will be maximized, not of the ensemble. That guarantees the maximal distribution of different conformers during these searches.
Once the final ensemble is found and if you know how many rotamers per
conformer you have (assuming a constant number, like the tert-butyl
case), one can reset that number by using READENSEMBLE "ensemble.xyz"
to read it and CONFDEGEN to set a degeneracy. In the previous example
that would be CONFDEGEN 19683 and would give you the desired
\(\Delta G_{\rm conf}\) for that given ensemble.
6.4.5.1. Finding rotamers automatically¶
It is always possible to switch on the automatic search for rotamers and
their degeneracy by setting CONFDEGEN AUTO if that is what you want.
They will be added to the ensemble instead of being filtered out and the full
ensemble will be saved in files named .confrot.xyz.
Another approach would be to assume that, since the algorithm might find
all rotamers for some conformers but not for all, one might set the
degeneracy of all equal to the maximum value found so far (CONFDEGEN AUTOMAX). Let’s take as
an example a system with a tert-butyl + a methyl group with 81 rotamers
per conformer. GOAT will hardly find 81 rotamers for every single
conformer, but if it finds them for one conformer, all the others will
also have that same number.
Please be aware that there are cases where different conformers might have different numbers of rotamers (e.g. decane or long alkyl chains), and these cases should be treated with care.
6.4.6. GOAT-EXPLORE: global minima of atomic clusters or topology-free free PES searches¶
In case you want to find the lowest energy conformer for a cluster or
don’t want to keep the initial topology at all, you can use the
!GOAT-EXPLORE option instead. This will possibly break all bonds and
find the lowest energy structure for that given set of atoms, be that a
nanoparticle or an organic molecule.
For instance, let’s find the minimum of an Au\(_8\) nanoparticle on the GFN1 PES, starting from just a random agglomeration of gold atoms:
!XTB1 GOAT-EXPLORE PAL16 #XTB version 6.4.0
%GOAT NWORKERS 16 END
* xyz 0 1
Au -1.39858 2.62611 -0.79278
Au -2.50552 -0.07122 0.67538
Au -0.52174 -2.57892 -0.02415
Au 0.78881 0.39733 0.21816
Au 1.21116 1.90621 -2.64617
Au -1.19205 -0.30099 -2.30429
Au -0.33808 -1.07129 2.90822
Au -0.85565 2.15342 2.41956
*
Please note that there is a minimum number of optimizations per worker
that must be respected in order for the algorithm to make sense.
Otherwise, on the limit, one optimization per worker would mean almost
nothing happens. This minimum number is max(N, 15) for the regular GOAT
and max(3N, 45) for GOAT-EXPLORE and GOAT-REACT (see below), where N is the number of atoms. The searches using free topology are more demanding because there are many more degrees of freedom.
When the minimum number of optimizations per worker is reached, the information is printed on the bottom of the header as:
GOAT version ... explore
Minimum global steps ... 3
Number of base workers ... 4
Split workers by ... 4
Final number of workers ... 16
Number of available CPUs ... 1
Parameter list (worker : temperature) ... 0 : 2903.97, 1 : 1451.98,
2 : 725.99, 3 : 363.00,
4 : 2903.97, 5 : 1451.98,
6 : 725.99, 7 : 363.00,
8 : 2903.97, 9 : 1451.98,
10 : 725.99, 11 : 363.00,
12 : 2903.97, 13 : 1451.98,
14 : 725.99, 15 : 363.00
GradComp (mean : sigma) ... 1.00 : 0.50
Number of atoms ... 8
Number of fragments ... 1
Flexibility parameter ... 1.00
Optimizations per global step ... 528
Optimizations per worker ... 66
*Reached the minimum optimizations per worker [fmax(3 * NAtoms, 45)]!
The global minimum found is a \(D_{4h}\) planar structure, the same as found on the literature for the Au\(_8\) cluster using other DFT methods [54]:
Fig. 6.27 The lowest energy conformer of the Au\(_8\) cluster on the GFN1 PES.¶
6.4.7. GOAT-REACT: an algorithm for automatic reaction pathway exploration¶
Another variant of the GOAT algorithm was created to allow for automatic reaction exploration, which in the end is nothing more than an exploration on the collective PES of reactant and product.
Here the user can be really creative and there are many different ways to explore this algorithm, but let us start with a simple reaction: the gas phase reaction of ethylene and singlet oxygen.
Fig. 6.28 What could be the products of the reaction between ethylene and singlet oxygen?¶
After running the following input:
!XTB GOAT-REACT
* XYZ 0 1
C -3.26482 -0.47497 0.33191
C -2.16518 0.24269 0.35382
H -4.23539 -0.01923 0.27823
H -3.23979 -1.54754 0.37118
H -2.19035 1.31540 0.31866
H -1.19481 -0.21295 0.41157
O -3.42426 -0.30941 2.30779
O -2.17088 0.05188 2.32517
*
the output looks more or less similar to the regular GOAT-EXPLORE, except for a few differences:
The maximum barriers GOAT is allowed to cross are higher.
The very initial geometry optimization is skipped by default.
AUTOWALLis set toTRUEwhich means that an ellipsoid wall potential is added using the maximum x,y,z dimensions of the molecule + 5 Angs as radii.
Another important factor is the maximum topological difference (MAXTOPODIFF), which is set to 8 by default, as printed on the output:
Global parameters
-----------------
GOAT version ... react
Max. topological diff. ... 8
Minimum global steps ... 3
Number of base workers ... 4
MAXTOPODIFF is a key concept here. If one simply looks for all possible topological permutations between reactants and products, even simple systems such as this could lead to an enormous number of combinations.
We defined the topological difference simply as the sum of broken bonds + formed bonds from some reference structure, which is taken from the structure obtained after the first geometry optimization inside the GOAT iterations (before any uphill step).
There will be more files printed than usual, the most important ones are:
Basename.products.xyz– contains all reactomers and all their conformers for the reaction. It is usually a very large file.Basename.products.topodiff2.xyz– contains only those separated with topodiff 2 from the reference structure, and so on.Basename.products.unique.xyz– contains a list of all topologically unique products, without their conformers or rotamers, only the lowest energy conformer is printed. Here the reference structure will come first and the others will be shown with their relative energy difference in kcal/mol.
Some of the products found as an example for this reaction are:
Fig. 6.29 Some products automatically found by GOAT-REACT using the input given above.¶
Note
Please be aware that singlet oxygen is so reactive that even the first optimization leads to a cyclization reaction and the reaction product is then taken as the reference structure.
Important
The use of force-fields like the GFN-FF is not recommended here, because it is not supposed to break bonds.
6.4.8. Some general observations¶
6.4.8.1. Default frozen coordinates during uphill step¶
During the uphill phase only, by default GOAT will freeze:
all bonds,
all angles involving two sp2 atoms within the same ring,
all dihedrals around a strong bond (d(B,C) < [0.9 x (sum of covalent radii)]).
“sp2 atoms” are here loosely defined only for C, N and O with less than 4,3 and 2 bonds respectively.
The first freeze is to avoid change of topology by bond breaking. The second and third are to avoid going over very high energy barriers on changing these angles, which in practice, unless under very special circumstances will never flip anyway!
These constraints are automatically lifted for GOAT-EXPLORE and can also be set to FALSE with their specific keywords.
6.4.8.2. Parallelization of GOAT¶
GOAT will profit from a large number of cores in a different way than most ORCA jobs, because it distributes the necessary work along different workers. It can also work multidone and distribute these workers through different nodes.
Since there is usually a regular first optimization step before starting GOAT, which will not profit from a large number of cores, these are limited by the flag MAXCORESOPT and set to a maximum of 32. After that, GOAT will switch back to use all cores provided. We do not recommend changing that maximum number, because it will probably only make things slower, but it can be controlled inside the %GOAT block.
6.4.8.3. Tips and extra details¶
Note
GOAT will work with any method in ORCA, all you need is the gradient. That includes using DFT, QM/MM, ONIOM, broken-symmetry states, excited states etc.
Be aware that DFT is much costlier than XTB. It is perfectly possible to run GOAT with R2SCAN-3C, but be prepared to use many cores or wait for a few days :D. We recommend at least
%PAL NPROCS 32 END, to have 8 workers with 4 cores each. Hybrid DFT is even heavier, so if you want to use B3LYP,go with at leastNPROCS 64- and don’t hurry. The aim is to do a global search here, it does not come for free!In many cases, it might be useful to use
GFNUPHILL GFNFFto use the GFN-FF force-field PES during the uphill steps. There, an exact potential is not really needed as the main objective is to take structures out of their current minimum and GOAT will run much faster, only using the chosen method for the actual optimizations. GFN2XTB, GFN1XTB or GFN0XTB are also valid options.For methods that need bond breaking, such as
GOAT-EXPLOREorGOAT-REACT, GFNUPHILL GFNFF cannot be used because the GFN-FF will not allow for bond breaking. Choose GFN2XTB, GFN1XTB or GFN0XTB.You can always check what the workers are doing by looking into the
Basename.goat.x.x.outfiles. The first number refers to the global iteration and the second to the specific worker. This is an ORCA output (with some suppressed printing to save space) that can be opened in most GUIs.GOAT will automatically detect fragments at the very beginning, even before the first geometry optimization. It will also respect fragments given via the geometry blocks. You can turn this off by setting
AUTOFRAGtoFALSEunder%GOAT.Amide bond chirality is not frozen by default, which means the input topology you gave for amides (cis or trans) may change. If you want to freeze it, set
FREEZEAMIDEStoTRUE.Similarly double bonds outside rings can also change their topology. Choose
FREEZECISTRANS TRUEin order to freeze those dihedrals.For certain molecules, it might be interesting to limit the coordination number of certain atoms, in that case use
MAXCOORDNUMBER.GOAT will respect the choices from the
%GEOMblock for the geometries so you can use all kinds of constraints you need for other types of coordinate freeze. It can also be combined with all kinds of arbitrary wall potentials available (see Section 6.3.8).If you want to push only certain atoms uphill, you can give a list to
UPHILLATOMS. In that case the uphill force shown in Fig. 6.24 will be applied only to the coordinates involving those atoms and the rest of the molecule will only react to that. This is useful for conformational searches on parts of a bigger system.By default conformers up to 12.0 kcal/mol from the global minimum are included, this can be changed by setting
MAXEN.
6.4.9. Basic keyword list¶
Here we present a basic list of options to be given under %GOAT:
%GOAT
#
# general options
#
MAXITER 128 # defines an arbitrary number of max GOAT geom opt iters per worker.
MAXOPTITER 256 # maximum number of geometry optimizations per GOAT iter.
SKIPINITIALOPT TRUE # if you want to skip the initial optimization (default FALSE).
RANDOMSEED TRUE # set it to FALSE to have a deterministic GOAT run. since the
# geometry optimization can change due to numerical differences
# it might not be fully deterministic in some cases.
READENSEMBLE "name.xyz" # an ensemble file to be read. the comment line should
# have the format "Energy (float)", as generated by GOAT.
# nothing will be done, except that the filters
# will be reapplied.
AUTOWALL TRUE # automatically create an ellipsoid wall potential
# around the structure (+5 Angs)? (default is FALSE).
TEMPLIST 3000, 2000, 750, 500 # a list of temperatures, defines the number
# of basic workers, in Kelvin. do not change
# unless you know what to do.
MAXCORESOPT 32 # the max. number of cores used during the very first opt
#
# worker options
#
NWORKERS AUTO # define the number of workers (default AUTO).
# AUTO for an automatic ideal assignment,
# or give any number multiple of 4 (number of temperatures).
MAXITERMULT 3 # a simple keyword to multiply the number of geometry
# optimizations per worker. will quickly
# increase MAXITER.
KEEPWORKERDATA FALSE # set to TRUE to keep the worker outputs
# (might be a lot of data!).
WORKERRANDOMSTART TRUE # after the first cycle, each worker starts with a random
# structure from the previous set up to 3 kcal/mol
# instead of the lowest energy only.
# at least one starts from the lowest (default TRUE).
#
# uphill step
#
UPHILLATOMS {0:2 5 14:29} END # if given, only those atoms listed will be pushed,
# uphill others will just respond to it.
GFNUPHILL GFNFF # use GFN-FF only during the uphill steps? GFN2XTB, GFN1XTB or
# GFN0XTB are also valid options for the respective methods.
#
# filtering and screening
#
ALIGN FALSE # align all final conformers with respect to the
# lowest energy one?
ENDIFF 0.1 # minimum energy difference needed to differentiate
# conformers, in kcal/mol.
MAXEN 6.0 # the maximum relative energy of a conformer to
# be taken, in kcal/mol. 6 kcal/mol by default.
RMSD 0.125 # minimum RMSD to differentiate conformers, in Angstroem.
ROTCONSTDIFF 0.01 # maximum difference for the rotational constant, in %.
RMSDMETRIC EIGENVALUE # use eigenvalues of distance matrix for RMSD?
# default is RMSD in general
# and EIGENVALUE for GOAT-EXPLORE.
#
# entropy mode
#
MAXENTROPY FALSE # add delta Gconf as convergence criteria (default FALSE)?
CONFTEMP 298.15 # temperature used to compute the free energy, in Kelvin.
MINDELS 0.1 # the minimum entropy difference between two iterations
# to signal convergence, in cal/(molK).
CONFDEGEN 2 # set an arbitrary degeneracy per conformer?
AUTO # find that automatically based on the RMSD.
AUTOMAX # same as AUTO, but take the largest value as reference
# for all conformers.
#
# free topology
#
FREEHETEROATOMS FALSE # free all atoms besides H and C.
FREENONHATOMS FALSE # self explained.
FREEFRAGMENTS FALSE # free interfragment topology, i.e., bonds between fragments
might be formed or broken during the search but bonds
within the same fragment will be kept.
# we don't recommend changing these unless you really need to!
FREEZEBONDS FALSE # freeze bonds uphill (default TRUE)?
FREEZEANGLES FALSE # freeze sp2 angles and dihedrals uphill (default TRUE)?
FREEZECISTRANS FALSE # freeze cis-trans isomers outside rings (default FALSE)?
FREEZEAMIDES FALSE # freeze amide cis/trans chirality (default FALSE)?
MAXCOORDNUMBER 10, 4, 11, 6 # a list of "atom number, coordination number" that
# will define the maximum coordination number for
# those listed atoms, taken from distance-based criteria.
# in this case atom 10 will have a maximum of 4 and
# atom 11 a maximum of 6. others follow defaults.
#
# goat react
#
MAXTOPODIFF 8 # the maximum topological difference that is allow. Topodiff
# is simply defined based on number of broken + number of formed bonds
# using ORCA's regular distance based criteria [1.3 * (sum of Cov. Radii)]
END