International Workshop on 'New challenges in Reduced Density Matrix Functional Theory: Symmetries, time-evolution and entanglement'

September 26, 2017 to September 29, 2017
Location : CECAM-HQ-EPFL, Lausanne, Switzerland
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Analytic energy gradients, excited states, and pure-state N-representability in v2RDM-driven CASSCF

Eugene 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 [1]. 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 [2] 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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[5] M. Altunbulak and A. Klyachko, Commun. Math. Phys. 282 287 (2008).
[6] A. E. DePrince, III, J. Chem. Phys. 145 164109 (2016).