title: Cumulant reconstruction of the three-electron reduced density matrix in the anti-Hermitian contracted Schrödinger equation.
abstract: Differing perspectives on the accuracy of three-electron reduced-density-matrix (3-RDM) reconstruction in nonminimal basis sets exist in the literature. This paper demonstrates the accuracy of cumulant-based reconstructions, developed by Valdemoro (V) [F. Colmenero et al., Phys. Rev. A 47, 971 (1993)], Nakatsuji and Yasuda (NY) [Phys. Rev. Lett. 76, 1039 (1996)], Mazziotti (M) [Phys. Rev. A 60, 3618 (1999)], and Valdemoro-Tel-Perez-Romero (VTP) [Many-electron Densities and Density Matrices, edited by J. Cioslowski (Kluwer, Boston, 2000)]. Computationally, we extend previous investigations to study a variety of molecules, including LiH, HF, NH(3), H(2)O, and N(2), in Slater-type, double-zeta, and polarized double-zeta basis sets at both equilibrium and nonequilibrium geometries. The reconstructed 3-RDMs, compared with 3-RDMs from full configuration interaction, demonstrate in nonminimal basis sets the accuracy of the first-order expansion (V) as well as the important role of the second-order corrections (NY, M, and VTP). Calculations at nonequilibrium geometries further show that cumulant functionals can reconstruct the 3-RDM from a multireferenced 2-RDM with reasonable accuracy, which is relevant to recent multireferenced formulations of the anti-Hermitian contracted Schrodinger equation (ACSE) and canonical diagonalization. Theoretically, we perform a detailed perturbative analysis of the M functional to identify its second-order components. With these second-order components we connect the M, NY, and VTP reconstructions for the first time by deriving both the NY and VTP functionals from the M functional. Finally, these 3-RDM reconstructions are employed within the ACSE [D. Mazziotti, Phys. Rev. Lett. 97, 143002 (2006)] to compute ground-state energies which are compared with the energies from the contracted Schrodinger equation and several wave function methods.
authors.affiliation: Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: A Eugene
authors.initials: AE
authors.lastname: DePrince
authors.forename: David A
authors.initials: DA
authors.lastname: Mazziotti
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004583:Electrons; D004735:Energy Transfer; D006858:Hydrofluoric Acid / Q000737:chemistry; D007700:Kinetics; D018020:Lithium Compounds / Q000737:chemistry; D008956:Models, Chemical; D009584:Nitrogen / Q000737:chemistry; D011789:Quantum Theory; D014867:Water / Q000737:chemistry
chemical_list: D018020:Lithium Compounds; D014867:Water; D009584:Nitrogen; D006858:Hydrofluoric Acid