52 research outputs found
Time-Resolved X-ray Absorption Spectroscopy: An MCTDH Quantum Dynamics Protocol
No full textExpressions for linear and nonlinear spectroscopy simulation in the X-ray window in which the time evolution of a photoexcited molecular system is treated via quantum dynamics are derived. By leveraging on the peculiar properties of core-excited/ionized states, first- and third-order response functions are recast in the limit of time-scale separation between the extremely short core-state lifetime and the (comparably longer) electronic-state transfer and nuclear vibrational motion. This work is a natural extension of Segatta et al. (J. Chem. Theory Comput. 2023, 19, 2075-2091), in which some of the present authors coupled MCTDH quantum dynamics to spectroscopy simulation at different levels of sophistication. Full quantum dynamics and approximate expressions are compared by simulating X-ray transient absorption spectroscopy at the carbon K-edge in the pyrene molecule
Soft X-ray Spectroscopy Simulations with Multiconfigurational Wave Function Theory: Spectrum Completeness, Sub-eV Accuracy, and Quantitative Reproduction of Line Shapes
No full textMultireference methods are known for their ability to accurately treat states of very different nature in many molecular systems, facilitating high-quality simulations of a large variety of spectroscopic techniques. Here, we couple the multiconfigurational restricted active space self-consistent field RASSCF/RASPT2 method (of the CASSCF/CASPT2 methods family) to the displaced harmonic oscillator (DHO) model, to simulate soft X-ray spectroscopy. We applied such an RASSCF/RASPT2+DHO approach at the K-edges of various second-row elements for a set of small organic molecules that have been recently investigated at other levels of theory. X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) are simulated with a sub-eV accuracy and a correct description of the spectral line shapes. The method is extremely sensitive to the observed spectral shifts on a series of differently fluorinated ethylene systems, provides spectral fingerprints to distinguish between stable conformers of the glycine molecule, and accurately captures the vibrationally resolved carbon K-edge spectrum of formaldehyde. Differences with other theoretical methods are demonstrated, which show the advantages of employing a multireference/multiconfigurational approach. A protocol to systematically increase the number of core-excited states considered while maintaining a contained computational cost is presented. Insight is eventually provided for the effects caused by removing core-electrons from a given atom in terms of bond rearrangement and influence on the resulting spectral shapes within a unitary orbital-based framework for both XPS and XANES spectra
Quantum Chemical Modeling of the Photoinduced Activity of Multichromophoric Biosystems
No full textMultichromophoric biosystems represent a broad family with very diverse members, ranging from light-harvesting pigment-protein complexes to nucleic acids. The former are designed to capture, harvest, efficiently transport, and transform energy from sunlight for photosynthesis, while the latter should dissipate the absorbed radiation as quickly as possible to prevent photodamages and corruption of the carried genetic information. Because of the unique electronic and structural characteristics, the modeling of their photoinduced activity is a real challenge. Numerous approaches have been devised building on the theoretical development achieved for single chromophores and on model Hamiltonians that capture the essential features of the system. Still, a question remains: is a general strategy for the accurate modeling of multichromophoric systems possible? By using a quantum chemical point of view, here we review the advancements developed so far highlighting differences and similarities with the single chromophore treatment. Finally, we outline the important limitations and challenges that still need to be tackled to reach a complete and accurate picture of their photoinduced properties and dynamics
X-ray linear and non-linear spectroscopy of the ESCA molecule
No full textLinear and nonlinear X-ray spectroscopy hold the promise to provide a complementary tool to the available ample body of terahertz to UV spectroscopic techniques, disclosing information about the electronic structure and the dynamics of a large variety of systems, spanning from transition metals to organic molecules. While experimental free electron laser facilities continue to develop, theory may take the lead in modeling and inspiring new cutting edge experiments, paving the way to their future use. As an example, the not-yet-available two-dimensional coherent X-ray spectroscopy (2DCXS), conceptually similar to 2D-NMR, is expected to provide a wealth of information about molecular structure and dynamics with an unprecedented level of detail. In the present contribution, we focus on the simulation of linear and non-linear (2DCXS) spectra of the ESCA molecule. The molecule has four inequivalent carbon K-edges and has been widely used as a benchmark for photoelectron spectroscopy. Two theoretical approaches for the computation of the system manifold of states, namely, TDDFT and RASSCF/RASPT2, are compared, and the possible signals that may appear in a 2DCXS experiment and their origin are surveyed
Manipulating Core Excitations in Molecules by X-Ray Cavities
No full textCore excitations on different atoms are highly localized and therefore decoupled. By placing molecules in an x-ray cavity the core transitions become coupled via the exchange of cavity photons and form delocalized hybrid light-matter excitations known as core polaritons. We demonstrate these effects for the two inequivalent carbon atoms in 1,1-difluoroethylene. Polariton signatures in the x-ray absorption, two-photon absorption, and multidimensional four-wave mixing signals are predicted
Spectroscopy from quantum dynamics: a mixed wave function/analytical line shape functions approach
No full textQuantum dynamics is the natural framework in which accurate simulation of spectroscopy of nonadiabatically coupled molecular systems can be obtained. Even if efficient quantum dynamics approaches have been developed, the number of degrees of freedom that need to be considered in realistic systems is typically too high to explicitly account for all of them. Moreover, in open-quantum systems, a quasi-continuum of low-frequency environment modes need to be included to get a proper description of the spectral bands. Here, we describe an approach to account for a large number of modes, based on their partitioning into two sets: a set of dynamically relevant modes (so-called active modes) that are treated explicitly in quantum dynamics, and a set of modes that are only spectroscopically relevant (so-called spectator modes), treated via analytical line shape functions. Linear and nonlinear spectroscopy for a realistic model system is simulated, providing a clear framework and domain of applicability in which the introduced approach is exact, and assessing the error introduced when such a partitioning is only approximate
Gestione del rischio e decision making: il ruolo della creatività
No full textLa gestione del rischio è un aspetto cruciale in tutte le fasi del ciclo di vita poiché è legata alla capacità di prendere decisioni in maniera funzionale. Questo diventa ancora più importante in età adulta e anziana, quando ci si trova ad affrontare più frequentemente situazioni che richiedono l’assunzione di rischi. Il contributo presenta i risultati di due studi. Il primo, condotto su 185 soggetti italiani sani (18-81 anni; M=39.9; DS=17.8), presenta i dati relativi alla relazione tra propensione al rischio (Domain-Specific Risk-Taking), stili di decisione (General Decision Making Style) e creatività
Efficacy of a combination of natural lipid lowering agent in hypercholesterolemic patients.
No full textCharacterization of the PCDD/F in the Province of Trento
No full textAbstractThis paper aims to improve the already existing literature data on air concentrations of polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs). Four monitoring campaigns were carried out between 2002 and 2010 near Trento, a town in the North of Italy. These campaigns showed relatively low PCDD/F concentrations, in line with the values found in other Italian urban and industrial sites. Typical values for agricultural regions were measured in rural areas, with an increase during winter, possibly due to biomass burning. No critical situations were detected along an important highway, in spite of the non-negligible emission factors for traffic reported in the literature
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