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Latest developments in multiconfigurational range-separated density-functional theory: on many-body perturbation theory and actinide chemistry

Emmanuel Fromager

Center for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø, 9037 Tromsø, NORWAY, http://www.ctcc.uit.no/people/manu/

A progress report on the development of multiconfigurational range-separated DFT, simply referred to as short-range DFT (srDFT) in the following, is presented. Two different topics are addressed.

(i) The description of dispersion interaction effects in srDFT by means of self-consistent many-body perturbation theory techniques. A general formalism (i.e.valid for any zeroth-order hamiltonian), which is based on the one-electron reduceddensity matrix, is proposed for the derivation of computable expressions through any order of perturbation [1]. Two applications are then presented:the derivation of a second-order Moeller-Plesset-type one-electron reduced density matrix and a range-separated optimized effective potential method based on second-order Goerling-Levy-type perturbation theory.

(ii) The application of a Multi-Configurational Self-Consistent Field-srDFT (MCSCF-srDFT) approach to actinide chemistry. We focuse on the neptunyl (VII)NpO2+++ ion which has, according to wave-function theory-based calculations, a linear equilibrium geometry. However, due to significant static correlationeffects, standard functionals such as LDA, PBE or B3LYP give anequilibrium geometry that is bent. We address this bending problem within the MCSCF-srDFT approach [2].

References

[1] E. Fromager and H. J. Aa. Jensen, submitted to Phys. Rev. A (2008). "Self-consistent many-body perturbation theory in range-separated density-functional theory: a one-electron reduced density matrix-based formulation"

[2] E. Fromager, F. Real, P. Waahlin, U. Wahlgren and H. J. Aa. Jensen, to be submitted to J. Chem. Phys. (2008). "On the universality of the long/short-rangeseparation inmulticonfigurational density-functional theory. II. Investigating f0 actinide species"

Conical Intersections in TDDFT

Mark E. Casida

Laboratoire de Chimie Théorique, Département de Chimie Molécularie (DCM, UMR CNRS/UJF 5250), Institut de Chimie Moléculaire de Grenoble (ICMG, FR-2607), Université Joseph Fourier (Grenoble I), 301 rue de la Chimie, BP 53, F-38041 Grenoble Cedex 9, FRANCE, mark.casida@ujf-grenoble.fr, http://dcm.ujf-grenoble.fr/PERSONNEL/CT/casida/

Over 20 years ago, Runge and Gross proved that the external potential is determined up to an additive spatially-constant function of time by the time-dependent charge density and the initial wave function (which is itself a functional of thedensity if the system starts in its ground stationary state). [RG84] About a decade ago, the linear response form of time-dependent density-functional theory (LR-TDDFT) was introduced into quantum chemistry as a formally rigorous way to obtain information about excited states [C95] and, with few exceptions, has now become the dominant single-determinant method for treating excited states in medium- and large-sized molecules. This has led to obvious hopes that LR-TDDFT could also be used to model photochemical reactions. [C01] However it became clear in the 1990s that many (if not most)photochemical reactions pass through conical intersections (CXs) and many of these have biradicloid character which is normally not easily described by DFT. In fact, Levine et al. have argued that (S0,S1) CXs cannot occur in TDDFT in the adiabatic approximation. Their reasoning will be reviewed and the results of our investigation of the ability of TDDFT to describe a critical (S0,S1) CX in oxirane will be presented. [CDI+07,TTR+08] Important issues will be raised concerning holes below the Fermi level, how to treat two-electron excitations explicitly, and where a multiconfigurational TDDFT could be useful.

References

[RG84] E. Runge and E.K.U. Gross, Phys. Rev. Lett. 52, 997 (1984)."Density functional theory for time-dependent systems"

[C95] M.E. Casida in Recent Advances in Density Functional Methods, Part I, D.P. Chong, editor (World Scientific:Singapore, 1995), p. 155."Time-dependent density-functional response theory for molecules"

[C01] M.E. Casida, in Accurate Description of Low-Lying Molecular States and Potential Energy Surfaces, ACS Symposium Series 828, edited by Mark R. Hoffmann and Kenneth G. Dyall (ACS Press: Washington, D.C., 2002), ISBN 0-8412-3792-1, (Proceedings of ACS Symposium, San Diego, Calif., 2001), pp. 199-220."Jacob's ladder for time-dependent density-functional theory: Some rungs on the way to photchemical heaven"

[LKQM06] B.G. Levine, C. Ko, J. Quenneville, and T.J. Martinez, Molec. Phys. 104, 1039 (2006)."Conical intersections and double excitations in time-dependent density functional theory"

[CDI+07] F. Cordova, L.J. Doriol, A. Ipatov, M.E. Casida, C. Filippi, and A. Vela, J. Chem. Phys. 127, 164111 (2007)."Troubleshooting time-dependent density-functional theory for photochemical applications"

[TTR+08] E. Tapavicza, I. Tavernelli, U. Röthlisberger, C. Filippi, and M.E. Casida, in preparation."Mixed time-dependent density-functional theory/classical trajectory surface hopping study of oxirane photochemistry"

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