title: Strongly correlated barriers to rotation from parametric two-electron reduced-density-matrix methods in application to the isomerization of diazene.
abstract: Recently, parameterization of the two-electron reduced density matrix (2-RDM) has made possible the determination of electronic energies with greater accuracy and lower cost than traditional electron-pair theories including coupled cluster with single and double excitations [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)]. We examine the method's performance for strongly correlated barriers to rotation; in particular, we study two distinct pathways in the isomerization of diazene (N(2)H(2)) from cis to trans: (i) a strongly correlated rotational pathway and (ii) a moderately correlated inversion pathway. While single reference wavefunction methods predict that the rotational barrier is higher than the inversional barrier, the parametric 2-RDM method predicts that the rotational barrier is lower than the inversional barrier by 3.1 kcal/mol in the extrapolated basis set limit. The parametric 2-RDM results are in agreement with those from multireference methods including multireference perturbation theory and the solution to the anti-Hermitian contracted Schrödinger equation. We report energies, optimized structures, and natural orbital occupation numbers for three diazene minima and two transition states.
authors.affiliation: Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Sand
authors.forename: Christine A
authors.initials: CA
authors.lastname: Schwerdtfeger
authors.forename: David A
authors.initials: DA
authors.lastname: Mazziotti
mesh_terms: D000465:Algorithms; D004583:Electrons; D004735:Energy Transfer; D007094:Imides / Q000737:chemistry*; D011789:Quantum Theory; D012399:Rotation; D013237:Stereoisomerism
chemical_list: D007094:Imides; C038867:diazene