@misc{indiciae1a4133a44328,
  title = {Nonorthogonal density-matrix perturbation theory.},
  author = {Anders M N Niklasson and Valéry Weber and Matt Challacombe},
  year = {2005},
  doi = {10.1063/1.1944725},
  url = {https://pubmed.ncbi.nlm.nih.gov/16095346/},
  note = {Source identifier: 16095346}
}