@article{perdew1996,
  title={Generalized Gradient Approximation Made Simple},
  author={John P. Perdew and Kieron Burke and Matthias Ernzerhof},
  year={1996},
  journal={Physical Review Letters},
  doi={10.1103/physrevlett.77.3865},
  url={https://doi.org/10.1103/physrevlett.77.3865}
}