Light-matter interactions within the Ehrenfest–Maxwell–Pauli–Kohn–Sham framework: fundamentals,implementation, and nano-optical applications

In recent years significant experimental advances in nano-scale fabrication techniques and in available light sources have opened the possibility to study a vast set of novel light-matter interaction scenarios, including strong coupling cases. In many situations nowadays, classical electromagnetic modeling is insufficient as quantum effects, both in matter and light, start to play an important role. Instead, a fully self-consistent and microscopic coupling of light and matter becomes necessary. We provide here a critical review of current approaches for electromagnetic modeling, highlighting their limitations. We show how to overcome these limitations by introducing the theoretical foundations and the implementation details of a density-functional approach for coupled photons, electrons, and effective nuclei in non-relativistic quantum electrodynamics. Starting point of the formalism is a generalization of the Pauli–Fierz field theory for which we establish a one-to-one correspondence between external fields and internal variables. Based on this correspondence, we introduce a Kohn-Sham construction which provides a computationally feasible approach for ab-initio light-matter interactions. In the mean-field limit, the formalism reduces to coupled Ehrenfest–Maxwell–Pauli–Kohn–Sham equations. We present an implementation of the approach in the real-space real-time code Octopus using the Riemann–Silberstein formulation of classical electrodynamics to rewrite Maxwell's equations in Schrödinger form. This allows us to use existing very efficient time-evolution algorithms developed for quantum-mechanical systems also for Maxwell's equations. We show how to couple the time-evolution of the electromagnetic fields self-consistently with the quantum time-evolution of the electrons and nuclei. This approach is ideally suited for applications in nano-optics, nano-plasmonics, (photo) electrocatalysis, light-matter coupling in 2D materials, cases where laser pulses carry orbital angular momentum, or light-tailored chemical reactions in optical cavities just to name but a few.     

Titanium(IV) carboxylate complexes: Synthesis,structural characterization and cytotoxic activity

Four titanium(IV) carboxylate complexes [Ti(η⁵-C₅H₅)₂(O₂CCH₂SMes)₂] (1), [Ti(η⁵-C₅H₄Me)₂(O₂CCH₂SMes)₂] (2), [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)(O₂CCH₂SMes)₂] (3) and [Ti(η⁵-C₅Me₅)(O₂CCH₂SMes)₃] (4; Mes = 2,4,6-Me₃C₆H₂) have been synthesised by the reaction of the corresponding titanium derivatives [Ti(η⁵-C₅H₅)₂Cl₂], [Ti(η⁵-C₅H₄Me)₂Cl₂], [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)Cl₂] and [Ti(η⁵-C₅Me₅)Cl₃] and two (for 1–3) or three (for 4) equivalents of mesitylthioacetic acid. Complexes 1–4 have been characterized by spectroscopic methods and the molecular structure of the complexes 1, 2 and 4 have been determined by X-ray diffraction studies. The cytotoxic activity of 1–4 was tested against tumor cell lines human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, and normal immunocompetent cells, that is peripheral blood mononuclear cells PBMC and compared with those of the reference complexes [Ti(η⁵-C₅H₅)₂Cl₂] (R1), [Ti(η⁵-C₅H₄Me)₂Cl₂] (R2), [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)Cl₂] (R3) and cisplatin. In all cases, the cytotoxic activity of the carboxylate derivatives was higher than that of their corresponding dichloride analogues, indicating a positive effect of the carboxylato ligand on the final anticancer activity. Complexes 1–4 are more active against K562 (IC₅₀ values from 72.2 to 87.9 μM) than against HeLa (IC₅₀ values from 107.2 to 142.2 μM) and Fem-x cells (IC₅₀ values from 90.2 to 191.4 μM).     

The Sequential Building of Chiral Macrocyclic Bis‐β‐Lactams by Double Staudinger–Cu‐Catalyzed Azide–Alkyne Cycloadditions

A novel approach for the synthesis of macrocyclic bis‐β‐lactams based on the Cu‐catalyzed alkyne–azide cycloaddition (CuAAC) is reported. The procedure is general and allows access to a full range of diastereomerically or enantiomerically pure macrocyclic cavities in good yields. The incorporation of chiral oxazolidinone fragments at C3 in the β‐lactam rings allows the total enantiocontrol of the process.     

Influence of sialic acid and bacterial sialidase on differential adhesion of Pseudomonas aeruginosa to epithelial cells

Epithelial cell lines from several tissues show a differential sensitivity to Pseudomonas aeruginosa adherence. A549 (lung), HepG2 (liver) and Caco-2 (colon) cells presented an adhesion index of about 3, 1.5 and 5 CFU/cell, respectively, whereas Mz-Ch cell lines (gallbladder cholangiocytes) presented adhesion indexes up to 35. These variations could be associated with the variable amount of sialic acid in cell surface glycoconjugates. Moreover, the presence of free sialic acid in culture media induces the secretion by P. aeruginosa of a sialidase which is able to hydrolyze glycoconjugate-linked sialic acid. As shown with A549 cells, this specific hydrolysis increases bacterial adhesion, probably by unmasking new binding sites onto the cell surface.     

Effect of spin-orbit interaction on a magnetic impurity in the vicinity of a surface

We propose a new mechanism for surface-induced magnetic anisotropy to explain the thickness dependence of the Kondo resistivity of thin films of dilute magnetic alloys. The surface anisotropy energy, generated by spin-orbit coupling on the magnetic impurity itself, is an oscillating function of the distance d from the surface and decays as 1/d2. Numerical estimates based on simple models suggest that this mechanism, unlike its alternatives, gives rise to an effect of the desired order of magnitude.     

A new titanium building block for early-late heterometallic complexes; preparation of a new tetrameric metallomacrocycle by self assembly

The new titanium dicarboxylate complex Cp*TiMe(OOC)2py (2) [Cp*=eta5-C5Me5; (OOC)2py = 2,6-pyridinedicarboxylate] has been synthesized. The reaction of complex 2 with water renders [Cp*Ti(OOC)2py]2O (3). The molecular structure of 3 has been studied by X-ray diffraction methods. Complex 2 reacts with isocyanides to yield the respective iminoacyl derivatives Cp*Ti(eta2-MeCNR)(OOC)2py [R=tBu (4), 2,6-dimethylphenyl (xylyl) (5)]. The molecular structure of complex4 has been established by X-ray diffraction. Compound 2 has been employed as a new building block for the preparation of new early-late heterometallic compounds; it reacts with [M(mu-OH)(COD)]2 (M = Rh, Ir) to give the corresponding tetranuclear metallomacrocycle derivatives [Cp*Ti{(OOC)(2)py}(mu-O)M(COD)]2 [M = Rh (6); Ir (7)]. The molecular structure of 6 has been established by X-ray diffraction.     

Epitaxial growth of metals with high Ehrlich–Schwoebel barriers and the effect of surfactants

Interlayer diffusion in epitaxial systems with a high energy barrier at the atomic steps – the so-called Ehrlich–Schwoebel (ES) barrier – is strongly reduced. As a consequence of this, a continuous accumulation of roughness takes place during growth. This undesirable effect can be corrected by using surfactant agents. We have studied the influence of the ES barrier on the preparation of epitaxial films on Cu(111), and the surfactant effect of a monolayer of Pb. Received: 21 April 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999     

Determination of the emission rate of an Am–Be neutron source with a Bonner sphere spectrometer

The Neutron Measurements Laboratory of the Technical University of Madrid (LMN) has an automated panoramic irradiator with a 111 GBq ²⁴¹Am–Be neutron source installed in a bunker-type large room. This facility is going to be used for calibration purposes. Recently, a spectrometry campaign involving four research groups working with different Bonner Sphere Spectrometers (BSS) and using different spectral unfolding codes was carried out. As part of these measurements the emission rate, B(t), was estimated. The application of the generalized fitting method to account for the scattering contribution is difficult due to specific characteristics of the neutron installation. A reduced fitting method, which includes room-return and in-scatter, has instead been used to overcome this problem.Detailed Monte Carlo simulations (with MCNPX code) were also performed to estimate the fluence rate using the measured source strength value. This was performed at different points. Results were then compared with measurements.Finally, the ambient dose equivalent rate measured with a neutron monitor (LB6411) was compared with results using the BSS.     

Asymptotic Behaviour of λ-Convex Sets in the Hyperbolic Plane

It is known that the limit Area/Length for a sequence of convex sets expanding over the whole hyperbolic plane is less than or equal 1, and exactly 1 when the sets considered are convex with respect to horocycles. We consider geodesics and horocycles as particular cases of curves of constant geodesic curvature with 0 1 and we study the above limit Area/Length as a function of the parameter .