Efficient Computation of Two-Electron Reduced Density Matrices via Selected Configuration Interaction

Jeremy P. Coe, Andrés Moreno Carrascosa, Mats Simmermacher, Adam Kirrander, Martin J. Paterson

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)
42 Downloads (Pure)


We create an approach to efficiently calculate two-electron reduced density matrices (2-RDMs) using selected configuration interaction wavefunctions. This is demonstrated using the specific example of Monte Carlo configuration interaction (MCCI). The computation of the 2-RDMs is accelerated by using ideas from fast implementations of full configuration interaction (FCI) and recent advances in implementing the Slater-Condon rules using hardware bitwise operations. This method enables a comparison of MCCI and truncated CI 2-RDMs with FCI values for a range of molecules, which includes stretched bonds and excited states. The accuracy in energies, wavefunctions, and 2-RDMs is seen to exhibit a similar behavior. We find that MCCI can reach sufficient accuracy of the 2-RDM using significantly fewer configurations than truncated CI, particularly for systems with strong multireference character.

Original languageEnglish
Pages (from-to)6690-6699
Number of pages10
JournalJournal of Chemical Theory and Computation
Issue number11
Early online date5 Oct 2022
Publication statusPublished - 8 Nov 2022


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