title: Active-space N-representability constraints for variational two-particle reduced density matrix calculations.
abstract: The ground-state energy of a system of fermions can be calculated by minimizing a linear functional of the two-particle reduced density matrix (2-RDM) if an accurate set of N-representability conditions is applied. In this Letter we introduce a class of linear N-representability conditions based on exact calculations on a reduced active space. Unlike wave-function-based approaches, the 2-RDM methodology allows us to combine information from calculations on different active spaces. By adding active-space constraints, we can iteratively improve our estimate for the ground-state energy. Applying our methodology to a 1D Hubbard model yields a significant improvement over traditional 2-positivity constraints with the same computational scaling.
authors.affiliation: Department of Chemistry, Duke University, Durham, North Carolina 27708, USA. Neil.Shenvi@duke.edu
authors.forename: Neil
authors.initials: N
authors.lastname: Shenvi
authors.forename: Artur F
authors.initials: AF
authors.lastname: Izmaylov