Mazur, Grzegorz, et al. “Efficient Energy and Electrostatic Properties Calculations at the MP2 Theory Level: A Case Study of Density Matrix-Based Computational Quantum Chemistry”. Computing and Informatics, vol. 31, no. 3, Aug. 2012, p. 665-73, http://147.213.75.17/ojs/index.php/cai/article/view/1013.