We introduce a new class of exchange-correlation potentials for a static and time-dependent Density Functional Theory of strongly correlated systems in 3D. The potentials are obtained via Dynamical Mean Field Theory and, for strong enough interactions, exhibit a discontinuity at half filling density, a signature of the Mott transition. For time-dependent perturbations, the dynamics is described in the adiabatic local density approximation. Results from the new scheme compare very favorably to exact ones in clusters. As an application, we study Bloch oscillations in the 3D Hubbard model. 71.27.+a, 31.70.Hq, 71.10. Fd Time-dependent quantum phenomena hold an important place in today's condensed matter research. A major theoretical challenge in this field is to describe strongly correlated systems out of equilibrium.In the last decade, Time-Dependent Density Functional Theory (TDDFT) has gained favor as a computationally viable, in principle exact time-dependent description of materials [1,2]. The basic TDDFT variable is the one-particle density n and a key ingredient is the time-dependent exchange-correlation potential v xc , embodying the complexities of the many-body problem. TDDFT applied to strongly correlated systems is in its beginnings. Describing these systems in equilibrium with static density functional theory (DFT) [3] is already a difficult task [4]. TDDFT retains these difficulties, but also adds another hurdle: Since time enters explicitly the formulation, v xc depends on the history of n (memory effects) [1,2].In equilibrium, an effective ab-initio method to describe strong correlations is the LDA+DMFT [5,6], combining DFT in the local density approximation (LDA) with Dynamical Mean Field Theory (DMFT) [7]. DMFT, which treats correlations nonperturbatively via a local self-energy Σ [8], is also at the core of the DMFT+GW [9, 10], another ab-initio method, which deals with nonlocal correlations within the GW approximation [11]. These DMFT-based methods rely on Green's function formulations, and the practical feasibility (in a foreseeable future) of a nonequilibrium generalization is not easy to assess, since Green's-function propagation scales quadratically [12][13][14] with the simulation time.TDDFT dynamics involves only one time variable. It would thus be useful to have exchange-correlation potentials suitable for strongly correlated systems. In equilibrium, they could offer a better start for Green's function based ab-initio schemes. Out of equilibrium, they could be used for adiabatic LDA [15] dynamics via TDDFT and possibly be improved by including memory effects, absent in the adiabatic LDA.In this Letter we suggest a novel avenue to deal with strongly correlated systems in 3D and out of equilibrium, by combining DMFT with TDDFT. For model strongly correlated systems in 1D, exchange-correlation potentials for DFT were introduced [16,17], and a BetheAnsatz-based LDA (BALDA) for v xc was proposed. Such v BALDA xcwas then used to introduce an adiabatic scheme for the TDDFT of the 1D Hubbard m...

The interaction of electrons with quantized phonons and photons underlies the ultrafast dynamics of systems ranging from molecules to solids, and it gives rise to a plethora of physical phenomena experimentally accessible using time-resolved techniques. Green's function methods offer an invaluable interpretation tool since scattering mechanisms of growing complexity can be selectively incorporated in the theory. Currently, however, real-time Green's function simulations are either prohibitively expensive due to the cubic scaling with the propagation time or do neglect the feedback of electrons on the bosons, thus violating energy conservation. We put forward a computationally efficient Green's function scheme which overcomes both limitations. The numerical effort scales linearly with the propagation time while the simultaneous dressing of electrons and bosons guarantees the fulfillment of all fundamental conservation laws. We present a real-time study of the phonon-driven relaxation dynamics in an optically excited narrow band-gap insulator, highlighting the nonthermal behavior of the phononic degrees of freedom. Our formulation paves the way to first-principles simulations of electron-boson systems with unprecedented long propagation times.

Within the non-equilibrium Green's function (NEGF) formalism, the Generalized Kadanoff-Baym Ansatz (GKBA) has stood out as a computationally cheap method to investigate the dynamics of interacting quantum systems driven out of equilibrium. Current implementations of the NEGF-GKBA, however, suffer from a drawback: real-time simulations require noncorrelated states as initial states. Consequently, initial correlations must be built up through an adiabatic switching of the interaction before turning on any external field, a procedure that can be numerically highly expensive. In this work, we extend the NEGF-GKBA to allow for correlated states as initial states. Our scheme makes it possible to efficiently separate the calculation of the initial state from the real-time simulation, thus paving the way for enlarging the class of systems and external drivings accessible by the already successful NEGF-GKBA. We demonstrate the accuracy of the method and its improved performance in a model donor-acceptor dyad driven out of equilibrium by an external laser pulse. arXiv:1806.05639v1 [cond-mat.str-el]

The photochemistry of low lying excited states of six different fluorinated bromobenzenes has been investigated by means of femtosecond laser spectroscopy and high level ab initio CASSCF/CASPT2 quantum chemical calculations. The objective of the work was to investigate how and to what extent light substituents, position on the benzene ring and number, would influence the dissociation mechanism of bromobenzene. In general, the actual position of a fluorine atom affects the dissociation rate to a less extent than the number of fluorine atoms. A clear connection between a lowering of a repulsive pisigma relative to a bound pipi state and the number of fluorine substituents exists, and the previously suggested model of coupling between dissociation rate and relative location of bound and repulsive state still holds for these molecules. A more elaborate examination of the electronic structure of the excited states in bromobenzenes than previously reported is presented.

Quantum chemical calculations have been performed on the ground state and several low-lying excited states of bromobenzene, ortho-, meta-, and para-dibromobenzene, and 1,3,5-tribromobenzene using high-level ab initio and hybrid density-functional methods. Experimental observations of ultrafast predissociation in these molecules are clarified from extensive theoretical information about all low-energy potential-energy curves together with symmetry arguments. The intriguing observation that o- and m-dibromobenzene have two ultrafast predissociation channels while bromobenzene, p-dibromobenzene, and 1,3,5-tribromobenzene only have one such channel is explained from the calculated potential-energy curves. These show that the lowering of point-group symmetry from C2v to Cs along the main photodissociation reaction coordinate, which only occurs in o- and m-dibromobenzene, opens up a new predissociation channel. Dynamical quantum simulations based on the calculated potential-energy curves are used to estimate the coupling strength at the intersystem crossing point in bromobenzene.