Conspectus
Machine
learning has become a common and powerful tool in materials
research. As more data become available, with the use of high-performance
computing and high-throughput experimentation, machine learning has
proven potential to accelerate scientific research and technology
development. Though the uptake of data-driven approaches for materials
science is at an exciting, early stage, to realize the true potential
of machine learning models for successful scientific discovery, they
must have qualities beyond purely predictive power. The predictions
and inner workings of models should provide a certain degree of explainability
by human experts, permitting the identification of potential model
issues or limitations, building trust in model predictions, and unveiling
unexpected correlations that may lead to scientific insights. In this
work, we summarize applications of interpretability and explainability
techniques for materials science and chemistry and discuss how these
techniques can improve the outcome of scientific studies. We start
by defining the fundamental concepts of interpretability and explainability
in machine learning and making them less abstract by providing examples
in the field. We show how interpretability in scientific machine learning
has additional constraints compared to general applications. Building
upon formal definitions in machine learning, we formulate the basic
trade-offs among the explainability, completeness, and scientific
validity of model explanations in scientific problems. In the context
of these trade-offs, we discuss how interpretable models can be constructed,
what insights they provide, and what drawbacks they have. We present
numerous examples of the application of interpretable machine learning
in a variety of experimental and simulation studies, encompassing
first-principles calculations, physicochemical characterization, materials
development, and integration into complex systems. We discuss the
varied impacts and uses of interpretabiltiy in these cases according
to the nature and constraints of the scientific study of interest.
We discuss various challenges for interpretable machine learning in
materials science and, more broadly, in scientific settings. In particular,
we emphasize the risks of inferring causation or reaching generalization
by purely interpreting machine learning models and the need for uncertainty
estimates for model explanations. Finally, we showcase a number of
exciting developments in other fields that could benefit interpretability
in material science problems. Adding interpretability to a machine
learning model often requires no more technical know-how than building
the model itself. By providing concrete examples of studies (many
with associated open source code and data), we hope that this Account
will encourage all practitioners of machine learning in materials
science to look deeper into their models.