The `Molecule` Class¶

Note

While the Structure class focuses on crystals (repeating patterns), the Molecule class is for individual molecules.

Intro to the `Molecule` class¶

In chemistry, we often work with molecules like caffeine, aspirin, or water. In Simmate, these are represented by the Molecule class.

Under the hood, Simmate uses RDKit, but it provides a much simpler and more "Pythonic" interface for you to use.

Let's load the Molecule class:

from simmate.toolkit import Molecule

Summary of Steps¶

Working with molecules follows a similar pattern to structures:

Loading a molecule into Python (usually from SMILES or SDF)
Cleaning or modifying the molecule
Analyzing properties (weight, rings, LogP, etc.)
Visualizing or exporting the molecule

1. Load¶

The most common way to load a molecule is using a SMILES string, which is a text-based representation of a chemical structure.

Let's load Aspirin:

aspirin = Molecule.from_smiles("CC(=O)OC1=CC=CC=C1C(=O)O")

To see the molecule you just loaded:

print(aspirin)

Tip

If you're using Spyder or Jupyter, you can simply type aspirin and hit enter. Simmate will automatically show you a 2D image of the molecule!

2. Clean & Modify¶

Molecules often need 3D coordinates if you plan to run advanced simulations (like Quantum Espresso or VASP). By default, SMILES only gives you 2D connectivity.

i: Generating 3D Coordinates

You can "embed" the molecule to give it a rough 3D shape:

aspirin.convert_to_3d()

ii: Adding/Removing Hydrogens

Many file formats omit hydrogens to save space. You can add them back:

aspirin.add_hydrogens()

3. Analyze¶

The Molecule class has dozens of properties ready for you to use.

Basic properties:

aspirin.molecular_weight
aspirin.num_rings
aspirin.formula
aspirin.elements

Advanced properties:

Simmate also includes many predictors for common chemical properties:

aspirin.log_p_rdkit  # Partition coefficient
aspirin.tpsa_rdkit   # Polar surface area
aspirin.synthetic_accessibility  # How hard is it to make? (1-10)

4. Export¶

You can save your molecule to various formats. The most common is an SDF file, which stores the 3D coordinates and metadata.

aspirin.to_sdf_file("aspirin.sdf")

You can also save it as an image:

aspirin.to_png_file("aspirin.png")

Extra Tips & Tricks¶

Viewing in Spyder¶

Just like with Structure, you can use Spyder's variable explorer to see your Molecule objects.

Comparison¶

One of the best features of the Molecule class is that you can compare them directly. Simmate handles all the complex chemistry logic for you:

mol1 = Molecule.from_smiles("C")
mol2 = Molecule.from_smiles("C")
print(mol1 == mol2)  # Returns True!

The Molecule Class¶

Intro to the Molecule class¶