TY  - RPRT
TI  - Variational approach for approximating energy levels.
AU  - C Stubbins
AU  - K Das
PY  - 1993
DO  - 10.1103/physreva.47.4506
UR  - https://pubmed.ncbi.nlm.nih.gov/9909461/
ID  - 9909461
ER  -