Crystal Graph Convolutional Neural Networks

This software package implements the Crystal Graph Convolutional Neural Networks (CGCNN) that takes an arbitary crystal structure to predict material properties.

The package provides two major functions:

• Train a CGCNN model with a customized dataset.
• Predict material properties of new crystals with a pre-trained CGCNN model.

The following paper describes the details of the CGCNN framework:

Crystal Graph Convolutional Neural Networks for an Accurate and Interpretable Prediction of Material Properties

Table of Contents

• How to cite
• Prerequisites
• Usage
  • Define a customized dataset
  • Train a CGCNN model
  • Predict material properties with a pre-trained CGCNN model
• Authors
• License

How to cite

Please cite the following work if you want to use CGCNN.

@article{PhysRevLett.120.145301,
  title = {Crystal Graph Convolutional Neural Networks for an Accurate and Interpretable Prediction of Material Properties},
  author = {Xie, Tian and Grossman, Jeffrey C.},
  journal = {Phys. Rev. Lett.},
  volume = {120},
  issue = {14},
  pages = {145301},
  numpages = {6},
  year = {2018},
  month = {Apr},
  publisher = {American Physical Society},
  doi = {10.1103/PhysRevLett.120.145301},
  url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.145301}
}

Prerequisites

This package requires:

• PyTorch
• scikit-learn
• pymatgen

If you are new to Python, the easiest way of installing the prerequisites is via conda. After installing conda, run the following command to create a new environment named cgcnn and install all prerequisites:

conda upgrade conda
conda create -n cgcnn python=3.7 scikit-learn pytorch=1.0.0 torchvision pymatgen -c pytorch -c matsci

*Note: this code is tested for PyTorch v1.0.0+ and is not compatible with versions below v0.4.0 due to some breaking changes.

This creates a conda environment for running CGCNN. Before using CGCNN, activate the environment by:

source activate cgcnn

Then, in directory cgcnn, you can test if all the prerequisites are installed properly by running:

python main.py -h
python predict.py -h

This should display the help messages for main.py and predict.py. If you find no error messages, it means that the prerequisites are installed properly.

After you finished using CGCNN, exit the environment by:

source deactivate

Usage

Define a customized dataset

To input crystal structures to CGCNN, you will need to define a customized dataset. Note that this is required for both training and predicting.

Before defining a customized dataset, you will need:

• CIF files recording the structure of the crystals that you are interested in
• The target properties for each crystal (not needed for predicting, but you need to put some random numbers in id_prop.csv)

You can create a customized dataset by creating a directory root_dir with the following files:

1. id_prop.csv: a CSV file with two columns. The first column recodes a unique ID for each crystal, and the second column recodes the value of target property. If you want to predict material properties with predict.py, you can put any number in the second column. (The second column is still needed.)

2. atom_init.json: a JSON file that stores the initialization vector for each element. An example of atom_init.json is data/sample-regression/atom_init.json, which should be good for most applications.

3. ID.cif: a CIF file that recodes the crystal structure, where ID is the unique ID for the crystal.

The structure of the root_dir should be:

root_dir
├── id_prop.csv
├── atom_init.json
├── id0.cif
├── id1.cif
├── ...

There are two examples of customized datasets in the repository: data/sample-regression for regression and data/sample-classification for classification.

For advanced PyTorch users

The above method of creating a customized dataset uses the CIFData class in cgcnn.data. If you want a more flexible way to input crystal structures, PyTorch has a great Tutorial for writing your own dataset class.

Train a CGCNN model

Before training a new CGCNN model, you will need to:

• Define a customized dataset at root_dir to store the structure-property relations of interest.

Then, in directory cgcnn, you can train a CGCNN model for your customized dataset by:

python main.py root_dir

You can set the number of training, validation, and test data with labels --train-size, --val-size, and --test-size. Alternatively, you may use the flags --train-ratio, --val-ratio, --test-ratio instead. Note that the ratio flags cannot be used with the size flags simultaneously. For instance, data/sample-regression has 10 data points in total. You can train a model by:

python main.py --train-size 6 --val-size 2 --test-size 2 data/sample-regression

or alternatively

python main.py --train-ratio 0.6 --val-ratio 0.2 --test-ratio 0.2 data/sample-regression

You can also train a classification model with label --task classification. For instance, you can use data/sample-classification by:

python main.py --task classification --train-size 5 --val-size 2 --test-size 3 data/sample-classification

After training, you will get three files in cgcnn directory.

• model_best.pth.tar: stores the CGCNN model with the best validation accuracy.
• checkpoint.pth.tar: stores the CGCNN model at the last epoch.
• test_results.csv: stores the ID, target value, and predicted value for each crystal in test set.

Predict material properties with a pre-trained CGCNN model

Before predicting the material properties, you will need to:

• Define a customized dataset at root_dir for all the crystal structures that you want to predict.
• Obtain a pre-trained CGCNN model named pre-trained.pth.tar.

Then, in directory cgcnn, you can predict the properties of the crystals in root_dir:

python predict.py pre-trained.pth.tar root_dir

For instace, you can predict the formation energies of the crystals in data/sample-regression:

python predict.py pre-trained/formation-energy-per-atom.pth.tar data/sample-regression

And you can also predict if the crystals in data/sample-classification are metal (1) or semiconductors (0):

python predict.py pre-trained/semi-metal-classification.pth.tar data/sample-classification

Note that for classification, the predicted values in test_results.csv is a probability between 0 and 1 that the crystal can be classified as 1 (metal in the above example).

After predicting, you will get one file in cgcnn directory:

• test_results.csv: stores the ID, target value, and predicted value for each crystal in test set. Here the target value is just any number that you set while defining the dataset in id_prop.csv, which is not important.

Authors

This software was primarily written by Tian Xie who was advised by Prof. Jeffrey Grossman.

License

CGCNN is released under the MIT License.