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, https://www.cai.sk/ojs/index.php/cai/article/view/1013.