AutoAdsorbate is a lightweight and easy-to-use Python package for generating chemically meaningful configurations of molecules and fragments on surfaces. Built with minimal dependencies and a low barrier to entry, it enables rapid setup of surface-adsorbate systems using the Surrogate-SMILES (*SMILES) representation. Ideal for researchers in catalysis, nanotech, and materials science, AutoAdsorbate streamlines dataset generation for simulations and machine learning workflows.

The challenge of generating initial structures for heterogeneous catalysis has traditionally been addressed through manual effort. This package offers an alternative, automated approach.

To effectively simulate reactive behavior at surfaces, it is crucial to establish clear definitions within our framework. The following definitions are essential for accurately characterizing the structures of interest:

Fragment:
- Molecules – species that retain their corresponding geometries even when isolated from the surface.
- Reactive species – species that adopt their corresponding geometries only when attached to the surface.
Surface:
- The surface is defined simply – every atom of the slab that can be in contact with an intermediate is considered a surface atom. The surface is the collection of such atoms.
- Every atom of the surface is a "top" site.
- When two "top" sites are close (close in its literal meaning), they form a "bridge" site.
- When three "top" sites are close (close in its literal meaning), they form a "3-fold" site.
- etc.
Active Site:
- A collection of one or more sites that can facilitate a chemical transformation is called an active site.
- A "top" site can be an active site only for Eley-Rideal transformations.
- All other transformations require that at least one intermediate binds through at least two sites. All involved sites compose an active site.
Intermediate:
- Intermediates are fragments bound to an active site.

Fragment

Molecules and reactive species are both initialized as the Fragment object (based on ase.Atoms). Some examples are given bellow.

Molecules

Let us initialize a molecule of dimethyl ether (DME):

from autoadsorbate import Fragment

f = Fragment(smile = 'COC', to_initialize = 5)

from autoadsorbate import docs_plot_conformers

conformer_trajectory = f.conformers
fig = docs_plot_conformers(conformer_trajectory)

Notice that the orientation of the fragment is arbitrary. While we could simply place these structures onto the surface of a material, it would be difficult to evaluate the quality of these initial random configurations. This uncertainty would force us to sample a large number of structures and run dynamic simulations to explore local minima and determine which configurations are the most stable.

However, in the case of DME, we can leverage chemical intuition to simplify the problem. The oxygen atom bridging the two methyl groups has two lone electron pairs. By using a simple trick—replacing one of these lone pairs with a marker atom (such as chlorine, Cl)—we can guide the placement more effectively.

Notice that we had to make two adjustments to the SMILES string. To replace the lone pair with a marker atom, we must "trick" the valence of the oxygen atom and rearrange the SMILES formula so that the marker atom appears first (for easier bookkeeping). - COC original - CO(Cl)C add Cl instead of the O lone pair (this is an invalid SMILES) - C[O+](Cl)C trick to make the valence work - Cl[O+](C)C rearrange so taht the SMILES string starts with the marker first (for easy book keeping)

This can be also done with a function:

from autoadsorbate import get_marked_smiles
marked_smile = get_marked_smiles(['COC'])[0]
marked_smile

'Cl[O+](C)(C)'

These surrogate smilles san now be used to initialize a Fragment object (we can set the number of randoms conformers to be initialized):

f = Fragment(smile = 'Cl[O+](C)(C)', to_initialize = 5)
len(f.conformers)

We can visualize these structures:

from autoadsorbate import docs_plot_conformers

conformer_trajectory = f.conformers
fig = docs_plot_conformers(conformer_trajectory)

Now we can use the marker atom to orient our molecule:

from autoadsorbate import docs_plot_sites

oriented_conformer_trajectory = [f.get_conformer(i) for i, _ in enumerate(f.conformers)]
fig = docs_plot_conformers(oriented_conformer_trajectory)

We can also easily remove the marker:

clean_conformer_trajectory = [atoms[1:] for atoms in oriented_conformer_trajectory]
fig = docs_plot_conformers(clean_conformer_trajectory)

Reactive species

Methoxy

f = Fragment(smile = 'ClOC', to_initialize = 5)
oriented_conformer_trajectory = [f.get_conformer(i) for i, _ in enumerate(f.conformers)]
fig = docs_plot_conformers(oriented_conformer_trajectory)

Methyl

f = Fragment(smile = 'ClC', to_initialize = 5)
oriented_conformer_trajectory = [f.get_conformer(i) for i, _ in enumerate(f.conformers)]
fig = docs_plot_conformers(oriented_conformer_trajectory)

Frangments with more than one binding mode (e.g. 1,2-PDO)

bound through single site:

f = Fragment(smile = 'Cl[OH+]CC(O)C', to_initialize = 5)
oriented_conformer_trajectory = [f.get_conformer(i) for i, _ in enumerate(f.conformers)]
fig = docs_plot_conformers(oriented_conformer_trajectory)

Coordinated withboth hydroxil:

f = Fragment(smile = 'S1S[OH+]CC([OH+]1)C', to_initialize = 5)
oriented_conformer_trajectory = [f.get_conformer(i) for i, _ in enumerate(f.conformers)]
fig = docs_plot_conformers(oriented_conformer_trajectory)

Surface

Defining the surface of a slab may seem like a simple task, but different approaches can yield varying results depending on the context. When considering catalytic sites, we can define these as surface regions capable of binding a fragment. By using reasonable steric criteria—essentially asking, "Is there enough space for a molecule to bind to that site?"—we can identify all possible binding sites on the slab's surface. These sites can be classified as top, bridge, or multi-fold, depending on how many atoms surround the site.

As an example: First, we need to define a slab (any ase.Atoms object). A slab is an arrangement of atoms that represents the boundary between a material and another phase, such as gas, fluid, or another material. We can either read an existing slab, or a new slab:

from ase.build import fcc111
slab = fcc111('Cu', (4,4,4), periodic=True, vacuum=10)

Now we can initalize the Surface object which associates the constructed slab (ase.Atoms) with additional information required for placing Fragments. We can view which atoms are in the surface:

s = Surface(slab)
plot_atoms(s.view_surface(return_atoms=True))

Visualizing surface Cu atoms as Zn

We have access to all the sites info as a pandas dataframe:

s.site_df.head()

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	coordinates	connectivity	topology	n_vector	h_vector	site_formula
0	[0.0, 0.0, 16.252703415323644]	1	[48]	[-0.004670396521231514, -0.0031449903964026822...	[1.0, 0.0, 0.0]	{'Cu': 1}
1	[0.6381638700208592, 1.105332246430909, 16.252...	2	[48, 52]	[0.0006776311857337964, -0.010516809475472271,...	[-0.5000000000000001, -0.8660254037844387, 0.0]	{'Cu': 2}
2	[1.2763277400417168, 5.162938145598479e-16, 16...	2	[48, 49]	[-0.011576660085263627, -0.017987208564805915,...	[-1.0, 0.0, 0.0]	{'Cu': 2}
3	[1.2763277400417183, 0.7368881642872727, 16.25...	3	[48, 49, 52]	[-0.01272989568588465, 0.0042077202541598024, ...	[-0.5000000000000001, -0.8660254037844387, 0.0]	{'Cu': 3}
4	[1.2763277400417183, 2.210664492861818, 16.252...	1	[52]	[0.0013334161774154326, -0.007734740595549886,...	[1.0, 0.0, 0.0]	{'Cu': 1}

or in dict form:

s.site_dict.keys()

dict_keys(['coordinates', 'connectivity', 'topology', 'n_vector', 'h_vector', 'site_formula'])

One can easily get access to sites as ase.Atoms as well, and find useful information in the ase.Atoms.info:

site_atoms = s.view_site(0, return_atoms=True)
site_atoms.info

{'coordinates': array([ 0.        ,  0.        , 16.25270342]),
 'connectivity': 1,
 'topology': [48],
 'n_vector': array([-0.0046704 , -0.00314499,  0.99998415]),
 'h_vector': array([1., 0., 0.]),
 'site_formula': {'Cu': 1}}

We can visualize a few surface sites:

from autoadsorbate import docs_plot_sites
fig = docs_plot_sites(s)

We can reduce the complete list of sites based on symmetry (ase.utils.structure_comparator.SymmetryEquivalenceCheck):

s.sym_reduce()
s.site_df

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	coordinates	connectivity	topology	n_vector	h_vector	site_formula
0	[0.0, 0.0, 16.252703415323644]	1	[48]	[-0.004670396521231514, -0.0031449903964026822...	[1.0, 0.0, 0.0]	{'Cu': 1}
1	[0.6381638700208592, 1.105332246430909, 16.252...	2	[48, 52]	[0.0006776311857337964, -0.010516809475472271,...	[-0.5000000000000001, -0.8660254037844387, 0.0]	{'Cu': 2}
3	[1.2763277400417183, 0.7368881642872727, 16.25...	3	[48, 49, 52]	[-0.01272989568588465, 0.0042077202541598024, ...	[-0.5000000000000001, -0.8660254037844387, 0.0]	{'Cu': 3}
8	[2.552655480083436, 1.4737763285745453, 16.252...	3	[49, 52, 53]	[-0.0011596349368944389, -0.001445905668587753...	[0.5000000000000002, -0.8660254037844385, 0.0]	{'Cu': 3}

We can again visualize the sites:

plot_atoms(s.view_surface(return_atoms=True))

Visualizing surface Cu atoms as Zn

Making surogate SMILES automatically

Simple methods of brute force SMILES enumeration are implemented as well. For example, only using a few lines of code we can initialize multiple conformers of all reaction intermediaries in the nitrogen hydrogenation reaction. A template of the required information can be found here:

from autoadsorbate import _example_config
_example_config

{'backbone_info': {'C': 1, 'N': 0, 'O': 2},
 'allow_intramolec_rings': True,
 'ring_marker': 2,
 'side_chain': ['(', ')'],
 'brackets': ['[', ']', 'H2]', 'H3]', 'H-]', 'H+]'],
 'make_labeled': True}

Now we can use (or edit) this information as we see fit:

from autoadsorbate import construct_smiles
 
config = {
'backbone_info': {'C': 0, 'O': 0, 'N':2},
'allow_intramolec_rings': True,
'ring_marker': 2,
'side_chain': ['(', ')'],
'brackets': ['[', ']', 'H+]', 'H2+]', 'H3+]'],
'make_labeled': True
}

smiles = construct_smiles(config)

We now have a list of surrgate SMILES that can be used to initalize Fragment objects.

smiles

['ClNN',
 'Cl[N]N',
 'Cl[NH+]N',
 'Cl[NH2+]N',
 'ClN[N]',
 'ClN[NH+]',
 'ClN[NH2+]',
 'ClN[NH3+]',
 'Cl[N][N]',
 'Cl[N][NH+]',
 'Cl[N][NH2+]',
 'Cl[N][NH3+]',
 'Cl[NH+][N]',
 'Cl[NH+][NH+]',
 'Cl[NH+][NH2+]',
 'Cl[NH+][NH3+]',
 'Cl[NH2+][N]',
 'Cl[NH2+][NH+]',
 'Cl[NH2+][NH2+]',
 'Cl[NH2+][NH3+]',
 'S1SN1N',
 'S1SNN1',
 'S1S[N]N1',
 'S1S[NH+]1N',
 'S1S[NH+]N1',
 'S1S[NH2+]N1',
 'S1SN1[N]',
 'S1SN1[NH+]',
 'S1SN1[NH2+]',
 'S1SN1[NH3+]',
 'S1S[N][N]1',
 'S1S[N][NH+]1',
 'S1S[N][NH2+]1',
 'S1S[NH+]1[N]',
 'S1S[NH+]1[NH+]',
 'S1S[NH+][NH+]1',
 'S1S[NH+]1[NH2+]',
 'S1S[NH+][NH2+]1',
 'S1S[NH+]1[NH3+]',
 'S1S[NH2+][NH2+]1',
 'ClN=N',
 'Cl[NH+]=N',
 'ClN=[N]',
 'ClN=[NH+]',
 'ClN=[NH2+]',
 'Cl[NH+]=[N]',
 'Cl[NH+]=[NH+]',
 'Cl[NH+]=[NH2+]',
 'S1SN=N1',
 'S1S[NH+]=N1',
 'S1S[NH+]=[NH+]1',
 'S1SN1#N']

from autoadsorbate import Fragment
 
trj = []
for s in smiles:
    try:
        f = Fragment(s, to_initialize=1)
        a = f.get_conformer(0)
        trj.append(a)
    except:
        pass
 
lst = [z for z in zip([a.get_chemical_formula() for a in trj],trj)]
lst.sort(key=lambda tup: tup[0])
trj =  [a[1] for a in lst]
len(trj)

From the list of initialized conformers we can remove the ones that are effectively identical:

from autoadsorbate import get_drop_snapped
 
xtrj = get_drop_snapped(trj, d_cut=1.5)
len(xtrj)

We can visualize these structures:

import matplotlib.pyplot as plt
from ase.visualize.plot import plot_atoms
from ase import Atoms
 
fig, axs = plt.subplots(3,11, figsize=[10,5], dpi=100)
 
for i, ax in enumerate(axs.flatten()):
    try:
        platoms = xtrj[i].copy()
         
    except:
        platoms = Atoms('X', positions = [[0,0,0]])
 
    for atom in platoms:
        if atom.symbol in ['Cl', 'S']:
            atom.symbol = 'Ga'
    plot_atoms(platoms, rotation=('-90x,0y,0z'), ax=ax)
    ax.set_axis_off()
    ax.set_xlim(-1, 5)
    ax.set_ylim(-0.5, 5.5)
 
fig.set_layout_engine(layout='tight')

Fully automatic - populate Surface with Fragment

A autonomous mode of Fragment placement on Surface is also implemented. The method tries to minimze the overlap of the Fragment and Surface while keeping the requested connectivity to the surface.

from ase.build import fcc211
from autoadsorbate import Surface, Fragment

slab = fcc211(symbol = 'Cu', size=(6,3,3), vacuum=10)  # any ase.Atoms object
s=Surface(slab, touch_sphere_size=2.7)                 # finding all surface atoms
s.sym_reduce()                                         # keeping only non-identical sites

fragments = [
    Fragment('S1S[OH+]CC(N)[OH+]1', to_initialize=20), # For each *SMILES we can request a differnet number of conformers 
    Fragment('Cl[OH+]CC(=O)[OH+]', to_initialize=5)    # based on how much conformational complexity we expect.
]

out_trj = []
for  fragment in fragments:
    out_trj += s.get_populated_sites(
      fragment,                    # Fragment object
      site_index='all',            # a single site can be provided here
      sample_rotation=True,        # rotate the Fragment around the surface-fragment bond?
      mode='heuristic',            # 'all' or 'heuristic', if heuristic surrogate smiles with 'Cl...' will be matched with top sites, etc. 
      conformers_per_site_cap=5,   # max number of conformers to sample
      overlap_thr=1.6,             # tolerated bond overlap betwen the surface and fragment      
      verbose=True
      )
    print('out_trj ', len(out_trj))

conformers 40
sites 9
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
WARNING: Failed to find requested number of conformers with condition: ovelap_thr = 1.6. Found 0 / 5. Consider setting a higher Fragment(to_initialize = < N >)
WARNING: Failed to find requested number of conformers with condition: ovelap_thr = 1.6. Found 1 / 5. Consider setting a higher Fragment(to_initialize = < N >)
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
WARNING: Failed to find requested number of conformers with condition: ovelap_thr = 1.6. Found 3 / 5. Consider setting a higher Fragment(to_initialize = < N >)
WARNING: Failed to find requested number of conformers with condition: ovelap_thr = 1.6. Found 0 / 5. Consider setting a higher Fragment(to_initialize = < N >)
out_trj  29
conformers 40
sites 3
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
SUCCESS! Found the requested numer of conformers with condition: ovelap_thr = 1.6. Found 5 / 5.
out_trj  44

Name		Name	Last commit message	Last commit date
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.github/workflows		.github/workflows
README_files		README_files
autoadsorbate		autoadsorbate
scripts		scripts
tests		tests
.gitignore		.gitignore
.python-version		.python-version
LICENSE		LICENSE
README.ipynb		README.ipynb
README.md		README.md
pyproject.toml		pyproject.toml
uv.lock		uv.lock

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Table of Contents

Installation

AutoAdsorbate

Fragment

Molecules

Reactive species

Methyl

Frangments with more than one binding mode (e.g. 1,2-PDO)

Surface

Making surogate SMILES automatically

Fully automatic - populate Surface with Fragment

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Installation

AutoAdsorbate

Fragment

Molecules

Reactive species

Methyl

Frangments with more than one binding mode (e.g. 1,2-PDO)

Surface

Making surogate SMILES automatically

Fully automatic - populate Surface with Fragment

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