erc: who: Head-Gordon, Martin what: Orbital-optimized opposite-spin scaled second order correlation: An economical method to improve the description of open-shell molecules when: 20070101 where: https://digital.library.unt.edu/ark:/67531/metadc927793/ erc-support: who: University of North Texas Libraries what: Permanent: Stable Content: when: 20081203 where: https://digital.library.unt.edu/ark:/67531/