Marjan Krstić

TURBOMOLE is a general-purpose quantum-chemical and materials science program suite for large-scale and high-throughput simulations of molecules and periodic systems of arbitrary dimensionality. The primary focus is on robust and highly efficient methods from first principles. Applications range from the interpretation or even prediction of various spectroscopic results to the elucidation of catalytic or reaction mechanisms. In this review, we summarize the latest developments between 2020 and 2026, consisting of substantial advances in density functional theory and coupled-cluster methods of ground and excited states, relativistic approaches for magnetic properties, and embedding or multiscale frameworks. In addition, the introduction of a new complete active space and configuration interaction module extends the capabilities of the program suite to multireference systems with strong static correlation. Finally, the user-friendliness was greatly improved with TURBOMOLE version 8.0 (2025) by new input formats and default settings making simulations easily possible for expert and non-expert users with a diverse chemical, physical, materials science, or biochemical education and training.

Second-harmonic generation (SHG) is a key nonlinear optical effect that only occurs in the absence of inversion symmetry. While centro-symmetric materials based on that definition would not sustain an SHG signal, the presence of an interface in a thin film can lead to a local deviation from the inversion symmetry and, hence, to a local second-order hyperpolarizability. To give rise to a notable SHG signal, the inversion symmetry needs to be broken at a global scale, suggesting that at least three materials must be stacked in an alternating manner when thin films are considered. Although such materials can be implemented with surface-anchored metal–organic frameworks (SURMOFs), their suitability for generating a strong second-order nonlinear response has remained unexplored so far. Here, we numerically investigate SHG from thin films of three different SURMOFs stacked above each other using a scale-bridging multi-scale framework combining precise quantum chemistry and fast Maxwell optical simulations. We determine the impact of the thickness of each SURMOF layer on the SHG signal. Our results indicate that interfaces between materials with similar SURMOF parameters contribute little to SHG, whereas interfaces to the surrounding dominate the response. Moreover, we demonstrate that the SHG signal can always be significantly boosted at specific total film thicknesses due to cavity resonances. At these resonances, reducing the individual layer thicknesses to the molecular scale, thereby allowing the film to behave as a bulk material composed almost entirely of interfaces, leads to a two-fold increase in the SHG signal compared to films with thicker layers. This introduces a trade-off between simpler fabrication and the enhanced SHG achievable with ultrathin layers. Our findings highlight the importance of interface effects in designing layered SURMOF structures with optimized nonlinear optical properties, offering guidance for future material explorations.

We introduce a basic formalism for computing thermal radiation by combining Waterman's T -matrix method with an algebraic approach to light-matter interactions. The formalism applies to nanoparticles, clusters thereof, and also molecules. In exemplary applications, we explore how a chiral structure can induce an imbalance in the circular polarization of thermal radiation. While the imbalance is rather small for a chiral molecule such as R-BINOL, a much larger imbalance is observed for an optimized silver helix of approximately 200 nm in size. Besides the directional Kirchhoff law used in this article, the formalism is suitable for implementing more nuanced theories, and also provides a straightforward path to the computation of thermal radiation spectra of astronomical objects moving at relativistic speeds with respect to the measurement devices.

It remains a prime question of how to describe the optical properties of large molecular clusters accurately. Quantum chemical methods capture essential electronic details but are infeasible for entire clusters, while optical simulations handle cluster-scale effects but miss crucial quantum effects. To overcome such limitations, we apply here a multi-scale modeling approach, combining precise quantum chemistry calculations with Maxwell scattering simulations, to study the linear and nonlinear optical response of finite-size supramolecular gold-cysteine nanoparticles dispersed in water. In this approach, every molecular unit that forms the cluster is represented by a polarizability and a hyperpolarizability, and the overall response is obtained from solving an optical multiple scattering problem. We particularly demonstrate how important it is to accurately consider the environment of the individual molecular units when computing their polarizability and hyperpolarizability. In our quantum chemical simulations, we do so at the level of a static partial charge field that represents the presence of other molecular units. Without correctly considering these effects of the embedding, predictions would deviate from experimental observations even qualitatively. Our findings pave the way for more accurate predictions of the optical response of complex molecular systems, which is crucial for advancing applications in nanophotonics, biosensing, and molecular optoelectronics.

Circularly polarized luminescence (CPL) in purely organic materials is limited by the almost exclusively electric nature of electronic transitions. Resolving this problem is possible through structuring organic materials at dimensions comparable to the wavelength of visible light. Here, the study explores the use of thin films made of chiral organic nanotubes for the enhanced induction of CPL. The study first performs multi‐scale modeling of the chiroptical properties of organic nanotubes using the T‐matrix method. Combined with chiroptical measurements, including Mueller matrix polarimetry, the study discusses the chiroptical properties of organic materials within the frames of their multi‐scale structuring. When embedding aggregation‐induced fluorogens (AIEgens) into the structured films, composites featured with gigantic g _lum factors reaching ≈10 ⁻¹ are obtained. Importantly, a series of control experiments is performed to exclude common parasitic effects that can lead to the apparent CPL signals. The enhanced chiroptical properties of the composite films of organic nanotubes and AIEgens enable visual discrimination of their handedness both in the absorption and emission realms. The uncovered multi‐mode enhancement of CPL directs future endeavors for anticounterfeiting or holography applications.

Second–harmonic generation (SHG) is forbidden in centrosymmetric materials. However, a signal is observed from interfaces where the symmetry is broken. Whereas the effect can be phenomenologically accommodated, a qualitative and quantitative description remained elusive, preventing the exploration of questions such as how deep below the surface the second–harmonic is generated. A multi–scale approach to compute the total and layer‐dependent intensity of surface SHG from molecular crystals is thus presented. The microscopic origin of surface SHG is identified in layer‐dependent models with embedding partial charges combined with density functional theory (DFT) showing symmetry‐breaking distortions of the electron cloud as the surface layer is approached. The SHG at the molecular level is determined using time‐dependent DFT and then brought to the macroscopic scale through a rigorous self‐consistent multiple scattering formalism. The intensity of the SHG at the surface layer is two orders of magnitude larger than at the next layer below and three orders of magnitude larger than two layers below. This approach can be used for designing and optimizing optical devices containing nonlinear molecular materials, such as molecular laminates. It is shown that a basic Kretschmann‐like setup can enhance the surface SHG of centrosymmetric molecular material a thousand times.

In the last few years, infrared reflection–absorption spectroscopy (IRRAS) has become a standard technique to study vibrational excitations of molecules. These investigations are strongly motivated by potential applications in monitoring chemical processes. For a better understanding of the adsorption mechanism of molecules on dielectrics, the polarization-dependence of an interaction of infrared light with adsorbates on dielectric surfaces is commonly used. Thus, the peak positions in absorption spectra could be different for s- and p-polarized light. This shift between the peak positions depends on both the molecule itself and the dielectric substrate. While the origin of this shift is well understood for infinite two-dimensional adsorbate layers, finite-size samples, which consist of 2D islands of a small number of molecules, have never been considered. Here, we present a study on polarization-dependent finite-size effects in the optical response of such islands on dielectric substrates. The study uses a multi-scale modeling approach that connects quantum chemistry calculations with Maxwell scattering simulations. We distinguish the optical response of a single molecule, a finite number of molecules, and a two-dimensional adsorbate layer. We analyze CO and CO₂ molecules deposited on CeO₂ and Al₂O₃ substrates. The evolution of the shift between the polarization-dependent absorbance peaks is first studied for a single molecule, which does not exhibit any shifting at all, and for finite molecular islands, where it increases with increasing island size, as well as for an infinite two-dimensional adsorbate layer. In the latter case, the agreement between the obtained results and the experimental IRRAS data and more traditional three/four-layer model theoretical studies supports the predictive power of the multi-scale approach.