GAtor: A First Principles Genetic Algorithm for Molecular Crystal Structure Prediction

TL;DR

GAtor is a parallel genetic algorithm implemented in Python for molecular crystal structure prediction, integrating machine learning and first principles DFT calculations to efficiently explore potential energy surfaces and identify low-energy crystal structures.

Contribution

The paper introduces GAtor, a novel genetic algorithm framework with evolutionary niching and machine learning clustering, enhancing exploration of complex molecular crystal energy landscapes.

Findings

Successfully predicted structures for four blind test targets.

Identified a novel $Z'$=2 structure for Target II.

Achieved structures consistent with experimental data.

Abstract

We present the implementation of GAtor, a massively parallel, first principles genetic algorithm (GA) for molecular crystal structure prediction. GAtor is written in Python and currently interfaces with the FHI-aims code to perform local optimizations and energy evaluations using dispersion-inclusive density functional theory (DFT). GAtor offers a variety of fitness evaluation, selection, crossover, and mutation schemes. Breeding operators designed specifically for molecular crystals provide a balance between exploration and exploitation. Evolutionary niching is implemented in GAtor by using machine learning to cluster the dynamically updated population by structural similarity and then employing a cluster-based fitness function. Evolutionary niching promotes uniform sampling of the potential energy surface by evolving several sub-populations, which helps overcome initial pool biases and selection biases (genetic drift). The various settings offered by GAtor increase the likelihood of locating numerous low-energy minima, including those located in disconnected, hard to reach regions of the potential energy landscape. The best structures generated are re-relaxed and re-ranked using a hierarchy of increasingly accurate DFT functionals and dispersion methods. GAtor is applied to a chemically diverse set of four past blind test targets, characterized by different types of intermolecular interactions. The experimentally observed structures and other low-energy structures are found for all four targets. In particular, for Target II, 5-cyano-3-hydroxythiophene, the top ranked putative crystal structure is a $Z^\prime$=2 structure with P$\bar{1}$ symmetry and a scaffold packing motif, which has not been reported previously.