TY  - RPRT
TI  - Density matrix perturbation theory.
AU  - Anders M N Niklasson
AU  - Matt Challacombe
PY  - 2004
DO  - 10.1103/physrevlett.92.193001
UR  - https://pubmed.ncbi.nlm.nih.gov/15169398/
ID  - 15169398
ER  -