The development of theories which accurately account for neardegeneracies and bond breaking, so called multireferencecorrelation, is a frontier of electronic structure.  A balance ofmoderate and strong electron correlation can be obtained fromsolving the anti-Hermitian part of the contracted Schrodingerequation (ACSE) for energies and two-electron density matrices(2-RDMs) without the many-electron wavefunction.  Cumulantreconctruction of the 3-RDM from the 2-RDM [Mazziotti, Chem. Phys.Lett. 289, 419 (1998)] removes the indeterminacy of the ACSE.Solution of the ACSE matches or exceeds the accuracy of traditionalmulti-reference wavefunction-based methods with polynomial scaling.  The ACSE has been applied to ground-state chemicalreactions including the electrocyclic ring-opening of bicyclobutaneand the sigmatropic shift of hydrogen in propene and acetone enolateas well as photoexcited reactions such as the ring-closing of allylradical and the ring-closing of gauche-1,3-butadiene via a conicalintersection.

Strongly correlated ground- and excited-state 2-RDMs from the anti-Hermtian contracted Schrodinger equation

242nd National Meeting (2011)

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