Experimental and Theoretical Study of the Ultrafast Dynamics of a Ni2 Dy2 -Compound in DMF After UV/Vis Photoexcitation.

We present a combined experimental and theoretical study of the ultrafast transient absorption spectroscopy results of a {Ni2 Dy2 }-compound in DMF, which can be considered as a prototypic molecule for single molecule magnets. We apply state-of-the-art ab initio quantum chemistry to quantitatively describe the optical properties of an inorganic complex system comprising ten atoms to form the chromophoric unit, which is further stabilized by surrounding ligands. Two different basis sets are used for the calculations to specifically identify two dominant peaks in the ground state. Furthermore, we theoretically propagate the compound's correlated many-body wavefunction under the influence of a laser pulse as well as relaxation processes and compare against the time-resolved absorption spectra. The experimental data can be described with a time constant of several hundreds of femtoseconds attributed to vibrational relaxation and trapping into states localized within the band gap. A second time constant is ascribed to the excited state while trap states show lifetimes on a longer timescale. The theoretical propagation is performed with the density-matrix formalism and the Lindblad superoperator, which couples the system to a thermal bath, allowing us to extract relaxation times from first principles.

Topological Spin-Charge Gearbox on a Real Molecular Magnet.

In this work, using ab initio many-body theory and inspired by an idea suggested by G. D. Mahan for an abstract N-dimensional chain composed of s-type atoms ( Phys. Rev. Lett. 2009, 102, 016801), we propose a functional topological spin-charge gearbox based on the real synthesized Co3Ni(EtOH) cluster driven with laser pulses. We analyze the implications arising from the use of a real molecule with d-character functional orbitals rather than an extended system and discuss the role of the point group symmetry of the system and the transferability of the electronic and spin density between different many-body states using specially designed laser pulses. We thus find that first-row transition-metal elements can host unpaired yet correlated d electrons and thus act as sites for spin information carriers, while designated laser pulses induce symmetry operations leading to a realizable spin-charge gearbox.

Ab initio theory for femtosecond spin dynamics, angle-resolved fidelity analysis, and the magneto-optical Kerr effect in the Ni3(CH3OH) and Co3(+)(CH3OH) clusters.

We present a systematic analysis of the ab initio controlled femtosecond spin dynamics in Ni3(CH3OH) and Co3(+)(CH3OH) clusters achieved by a spin-orbit-coupling enabled Λ process. The distortion caused by the attachment of CH3OH to one of the active magnetic centers of the Ni3 and the Co3(+) clusters induces asymmetric geometries which result in well localized spin densities on the magnetic centers. With the use of high-level quantum chemistry methods, successful spin-flip scenarios are demonstrated for both clusters. In order to assess the experimental accessibility of those effects, we compute their tolerance with respect to two laser pulse parameters, i.e., the energy detuning as well as the deviation of the polar angle ϕ from its optimized value. Finally, we calculate the magneto-optical Kerr effect in order to connect to the susceptibility tensor χ as an experimentally measurable quantity.

Combined theoretical and experimental study of spin and charge dynamics on the homodinuclear complex [Ni2(II)(L-N4Me2)(emb)].

We present a combined theoretical and experimental study of spin and charge dynamics on the homodinuclear compound [Ni2(II)(L-N4Me2)(emb)]. The theoretically calculated oscillator strengths of the ground-state absorption spectrum show an acceptable agreement with experiment. We predict a local ultrafast laser-induced spin-flip scenario, which involves charge-transfer states. Experimentally, we observe charge dynamics on two different time scales. The two relevant, transient electronic states and their electronic properties are also theoretically characterized. These results provide a joint investigation of the homodinuclear complex and suggest a realistic scenario for ultrafast spin dynamics and other optical-related manipulations.

Ab initio theory for ultrafast magnetic local spin flip on the newly synthesized homodinuclear complex [Ni(II)2(L-N4Me2)(emb)].

We present a fully ab initio calculation, the synthesis and the characterization of the homodinuclear [Ni(2)(II)(L-N(4)Me(2))(emb)] complex, which can act as a prototypic, realistic substance for ultrafast laser-induced spin dynamics. The new compound, which has been synthesized and characterized, consists of two magnetic centers with different spin properties and different local symmetries (distorted octahedral versus distorted square-planar) and exhibits strong spin localization. We calculate the vibrational and electronic spectra of the compound and predict a local spin-flip scenario. The very existence and the properties of the compound represent an important step toward ultrafast experimental spin dynamics in ligand-stabilized multicenter compounds and paves the path toward laser-induced magnetic logic on a single molecule.

Ab initio treatment of optical second harmonic generation in NiO.

In this Letter we develop a new systematic approach to study optical second harmonic generation in NiO, on both the (001) surface and the bulk. NiO is modeled as a doubly embedded cluster on which two highly correlated quantum chemistry methods are applied in order to obtain the wave functions of all the intragap d states and the low lying charge transfer states. The optical gap is calculated and the electric dipole, magnetic dipole, and electric quadrupole contributions to the second order susceptibility tensor are computed for the first time from first principles. Going beyond the electric dipole approximation gives new insight into the experimentally observed spectrum. A method is proposed for monitoring the spin dynamics of the NiO(001) surface.