International Workshop on 'New challenges in Reduced Density Matrix Functional Theory: Symmetries, time-evolution and entanglement'
Analytic energy gradients, excited states, and pure-state N-representability in v2RDM-driven CASSCFEugene DePrince
Florida State University, USA
The direct variational optimization of the ground-state two-electron reduced-density matrix (2-RDM) can routinely be achieved via semidefinite programming techniques. The resulting variational 2-RDM (v2RDM) approach can be used to realize polynomially-scaling complete active space self-consistent field (CASSCF) computations applicable to active spaces comprised of 50 electrons in 50 orbitals, or more . Analytic energy gradients for v2RDM-CASSCF are readily available, and excited-state information can be extracted from the time-evolution of the one-electron RDM  or within the framework of the extended random phase approximation (ERPA) [3,4]. However, within the ERPA, a proper treatment of excitations from degenerate ground states requires the application of pure-state N-representability conditions [5,6].
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