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The solvent effects on the linear and second-order nonlinear optical properties of an aminonaphtylethenylpyridinium (ANEP) dye are investigated by combining experimental and theoretical chemistry methods. On the one hand, deep near infrared (NIR) hyper-Rayleigh scattering (HRS) measurements (1840–1950 nm) are performed on solutions of di-8-ANEPPS in deuterated chloroform, dimethylformamide, and dimethylsulfoxide to determine their first hyperpolarizablity (βHRS). For the first time, these HRS experiments are carried out in the picosecond regime in the deep NIR with very moderate (≤3 mW) average input power, providing a good signal-to-noise ratio and avoiding solvent thermal effects. Moreover, the frequency dispersion of βHRS is investigated for Disperse Red 1 (DR1), a dye commonly used as HRS external reference. On the other hand, these are compared with computational chemistry results obtained by using a sequential molecular dynamics (MD) then quantum mechanics (QM) approach. The MD method allows accounting for the dynamical nature of the molecular structures. Then, the QM part is based on TDDFT/M06-2X/6-311+G* calculations using solvation models ranging from continuum to discrete ones. Measurements report a decrease of the βHRS of di-8-ANEPPS in more polar solvents and these effects are reproduced by the different solvation models. For di-8-ANEPPS and DR1, comparisons show that the use of a hybrid solvation model, combining the description of the solvent molecules around the probe by point charges with a continuum model, already achieves quasi quantitative agreement with experiment. These results are further improved by using a polarizable embedding that includes the atomic polarizabilities in the solvent description. [ABSTRACT FROM AUTHOR]

Recent measurements of the third harmonic scattering responses of molecules have given a new impetus for computing molecular second hyperpolarizabilities (γ) and for deducing structure–property relationships. This paper has employed a variety of wavefunction and density functional theory methods to evaluate the second hyperpolarizability of the p-nitroaniline prototypical push-pull π-conjugated molecule, addressing also numerical aspects, such as the selection of an integration grid and the impact of the order of differentiation vs the achievable accuracy by using the Romberg quadrature. The reliability of the different methods has been assessed by comparison to reference Coupled-Cluster Singles and Doubles with perturbative treatment of the Triples results. On the one hand, among wavefunction methods, the MP2 scheme offers the best accuracy/cost ratio for computing the static γ. On the other hand, using density functional theory, γ remains a challenging property to compute because all conventional, global hybrid or range-separated hybrid, exchange–correlation functionals underestimate static γ values by at least 15%. Even tuning the range-separating parameter to minimize the delocalization errors does not enable to improve the γ values. Nevertheless, the original double-hybrid B2-PLYP functional, which benefits from 27% of PT2 correlation and 53% Hartree–Fock exchange, provides accurate estimates of static γ values. Unfortunately, the best performing exchange–correlation functionals for γ are not necessarily reliable for the first hyperpolarizability, β, and vice versa. In fact, the β of p-nitroaniline (pNA) could be predicted, with a good accuracy, with several hybrid exchange–correlation functionals (including by tuning the range-separating parameter), but these systematically underestimate γ. As for γ, the MP2 wavefunction method remains the best compromise to evaluate the first hyperpolarizability of pNA at low computational cost. [ABSTRACT FROM AUTHOR]

The vibrational contributions to the average polarizability ( α ¯ ), to the second harmonic scattering (SHS) first hyperpolarizability (βSHS), and depolarization ratio (DRSHS), as well as to the third harmonic scattering (THS) second hyperpolarizability (γTHS) and depolarization ratio (DRTHS), have been evaluated for the water molecule using the Bishop and Kirtman perturbative theory approach, in combination with finite differentiation techniques to evaluate the higher-order derivatives. From a hierarchy of coupled cluster techniques and extended atomic basis sets, the CCSD/d-aug-cc-pVTZ level has been selected to assess the importance of the zero-point vibrational average (ZPVA) contributions and of the pure vibrational contributions with respect to their electronic counterparts. This is the first investigation demonstrating electronic and vibrational SHS, and THS responses can be computed for small molecules, with the perspective of performing comparisons with recent experimental data [Van Steerteghem et al., Anal. Chem. 89, 2964 (2017) and V. Rodriguez, J. Phys. Chem. C 121, 8510 (2017)]. Numerical results on the water molecule highlight that (i) the vibrational contributions to the dynamic α ¯ , βSHS, and γTHS are small but non negligible; (ii) they amount to 3%, 10%, and 4% at the typical 1064 nm wavelength, respectively; (iii) the mechanical anharmonicity term dominates the ZPVA contribution; (iv) the double harmonic terms dominate the pure vibrational contributions; (v) the stretching vibrations provide the largest contributions to the dynamic (hyper)polarizabilities; and (vi) these conclusions are strongly impacted in the static limit where the vibrational contributions are much larger, in particular the double harmonic pure vibrational terms, and even more in the case of the first hyperpolarizability. [ABSTRACT FROM AUTHOR]

This contribution employs quantum chemistry methods to describe the variations of the second nonlinear optical responses of molecular switches based on benzazolo-oxazolidine (BOX) units, connected by π-linkers, along their successive opening/closing. Under the fully closed forms, all of them display negligible first hyperpolarizability (β) values. When one BOX is opened, which is sketched as C→O, a push–pull π-conjugated segment is formed, having the potential to enhance β and to set the depolarization ratio (DR) to its one-dimensional-like value (DR = 5). This is observed when only one BOX is open, either for the monoBOX species (C→O) or for the diBOX (CC→CO) and triBOX (CCC→CCO) compounds, i.e., when the remaining BOXs stay closed. The next BOX openings have much different effects. For the diBOXs, the second opening (CO→OO) is associated with a decrease of β, and this decrease is tuned by controlling the conformation of the π-linker, i.e., the centrosymmetry of the whole compound because β vanishes in centrosymmetric compounds. For the triBOXs, the second opening gives rise to a Λ-shape compound, with a negligible change of β, but a decrease of the DR whereas, along the third opening, β remains similar and the DR decreases to the typical value of octupolar systems (DR = 1.5). [ABSTRACT FROM AUTHOR]

The static and dynamic first (β||) and second (γ||) hyperpolarizabilities of water, methanol, and dimethyl ether have been evaluated within the response function approach using a hierarchy of coupled cluster levels of approximation and doubly augmented correlation consistent atomic basis sets. For the three compounds, the electronic β|| and γ|| values calculated at the CCSD and CC3 levels are in good agreement with gas phase electric field-induced second harmonic generation (EFISHG) measurements. In addition, for dimethyl ether, the frequency dispersion of both properties follows closely recent experimental values [V. W. Couling and D. P. Shelton, J. Chem. Phys. 143, 224307 (2015)] demonstrating the reliability of these methods and levels of approximation. This also suggests that the vibrational contributions to the EFISHG responses of these molecules are small. [ABSTRACT FROM AUTHOR]

A combined experimental-theoretical investigation has revealed that oxazine-based compounds are multiaddressable, multistate, and multifunctional molecular switches exhibiting contrasts of both linear and second-order nonlinear optical properties. The switching properties are particularly large when the substituent is a donor group. In this study, the cleavage of the C-O bond at the junction of the indole and oxazine cycles (of the closed a forms) is acido-triggered, leading to an open form (b+) characterized by larger first hyperpolarizabilities (βHRS) and smaller excitation energies than in the closed form. These results are confirmed and interpreted utilizing ab initio calculations that have been carried out on a broad set of compounds to unravel the role of the substituent. With respect to acceptor groups, oxazines bearing donor groups are characterized not only by larger βHRS and βHRS contrast ratios but also by smaller excitation energies, larger opening-induced charge transfer, and reduction of the bond length alternation, as well as smaller Gibbs energies of the opening reaction. Compared to protonated open forms (b+), calculations on the zwitterionic open forms (b) have pointed out similarities in the long-wavelength UV/vis absorption spectra, whereas their βHRS values might differ strongly as a function of the substituent. Indeed, the open forms present two NLOphores, the indoleninium-substituent entity and the nitrophenol (present in the protonated open form, b+) or nitrophenolate (present in the zwitterionic open form, b) moiety. Then, nitrophenolate displays a larger first hyperpolarizability than nitrophenol and the β tensor of the two entities might reinforce or cancel each other. [ABSTRACT FROM AUTHOR]

In an attempt to design molecular electromechanical actuators with large deformation response, we present here three helicene-like compounds, which offer significant strain above 5 % due to two-electron charge transfer (CT). The shrinking induced by CT is a quantum mechanical orbital effect. A good π–π overlap across the helical pitch is critical for this type of actuation. The relevant overlap refers to frontier orbitals that are involved in the CT, and it has some features common with π–π stacking pancake bonds; however, these molecules do not represent all aspects of typical pancake bonding. This overlap is accompanied by a change in the bond length alternation pattern indicating significant change in π-conjugation. Additionally, two further helicene-like molecules included in this study also indicate large electromechanical actuation, but a simple orbital interpretation is not available in those cases. [ABSTRACT FROM AUTHOR]

The elaboration of multichromophoric system which can undergo a reversible transformation over more than two different states can be easily performed by the covalent assembly of several identical switching subunits around a central node. However, the selective addressability of each of them still represents a challenging task. This study reports on the elaboration of multichromophoric systems incorporating three identical indolino-oxazolidine (BOX) moieties as multimodal addressable units. Depending of the open/closed oxazolidine ring status of each of them, these systems can be interconverted between four different states in stepwise manner by using indifferently acid addition or electrochemical stimulation. More important, we have demonstrated by using a dissymmetric triarylamine node that the classical statistical BOX opening is broken then reaching a regioselective addressability. The switching of the three identical BOX units differentiated by their π conjugated junction to the central core follows a preferential order leading to the preponderant and successive formation of only four forms over the eight theoretically and equally expected. To provide limitations and outlooks for such strategy, their switching capacities have been rationalized by DFT calculations. [Display omitted] • The synthesis of new multichomophoric system exclusively based on BOX unit is proposed. • These multi-addressable systems can switch between four discrete levels exhibiting distinct optical properties. • The BOX opening of such multichromophoric system occur under stimulation in a preferential order [ABSTRACT FROM AUTHOR]

A computer-efficient model for underwater acoustic propagation in a shallow, three-dimensional rectangular duct closed at one end has been developed using the method of images. The duct simulates a turning basin located in a port, surrounded with concrete walls, and filled with sea water. The channel bottom is composed of silt. The modeled impulse response is compared with the impulse response measured between 15 kHz and 33 kHz. Despite small sensor-position inaccuracies and an approximated duct geometry, the impulse response can be modeled with a relative echo magnitude error of 1.62 dB at worst and a relative echo location error varying between 0% and 4% when averaged across multiple measurements and sensor locations. This is a sufficient level of accuracy for the simulation of an acoustic communication system operating in the same frequency band and in shallow waters, as time fluctuations in echo magnitude commonly reach 10 dB in this type of environment. [ABSTRACT FROM AUTHOR]

Acoustic networks of autonomous underwater vehicles (AUVs) cannot typically rely on protocols intended for terrestrial radio networks. This work describes a new location-aware source routing (LASR) protocol shown to provide superior network performance over two commonly used network protocols-flooding and dynamic source routing (DSR)-in simulation studies of underwater acoustic networks of AUVs. LASR shares some features with DSR but also includes an improved link/route metric and a node tracking system. LASR also replaces DSR's shortest-path routing with the expected transmission count (ETX) metric. This allows LASR to make more informed routing decisions, which greatly increases performance compared to DSR. Provision for a node tracking system is another novel addition: using the time-division multiple access (TDMA) feature of the simulated acoustic modem, LASR includes a tracking system that predicts node locations, so that LASR can proactively respond to topology changes. LASR delivers 2-3 times as many messages as flooding in 72% of the simulated missions and delivers 2-4 times as many messages as DSR in 100% of the missions. In 67% of the simulated missions, LASR delivers messages requiring multiple hops to cross the network with 2-5 times greater reliability than flooding or DSR [ABSTRACT FROM AUTHOR]

Acoustic communications and positioning are vital aspects of unmanned underwater vehicle operations. The usage of separate units on each vehicle has become an issue in terms of frequency bandwidth, space, power, and cost. Most vehicles rely on acoustic modems transmitting frequency-hopped multiple frequency-shift keyed sequences for command-and-control operations, which can be used to locate the vehicle with a good level of accuracy without requiring extra signal transmission. In this paper, an ultrashort baseline acoustic positioning technique has been designed, simulated, and tested to locate an acoustic modem source in three dimensions using a tetrahedral, half-wavelength acoustic antenna. The position estimation is performed using the detection sequence contained in each message, which is a series of frequency-hopped pulses. Maximum likelihood estimation of azimuth and elevation estimation is performed using a varying number of pulse and various signal-to-noise ratios. Simulated and measured position estimation error match closely, and indicate that the accuracy of this system improves dramatically as the number of pulses processed increases, given a fixed signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

The static and dynamic second harmonic (βSHS) and third harmonic (γTHS) scattering hyperpolarizabilities and depolarization ratios of water, carbon tetrachloride, chloroform, dichloromethane, chloromethane, and acetonitrile have been evaluated at the coupled cluster response theory level of approximation. Following two recent publications on their measurements, this is the first quantum chemical investigation on γTHS and on its decomposition into its spherical tensor components. Substantial electron correlation and basis set effects are evidenced for βSHS and γTHS and for their depolarization ratios, and they depend on the nature of the molecule. Then, using the selected CCSD/d-aug-cc-pVDZ level, the chlorinated methane derivatives have been studied, showing that (i) the γTHS response is dominated by its isotropic contribution, whereas (ii) for βSHS the dipolar contribution increases from carbon tetrachloride to dichloromethane, chloroform, chloromethane, and acetonitrile. Comparisons with the experimental data obtained from measurements in liquid phase (i) show that the increase of γTHS with the number for chlorine atoms is well reproduced by the calculations and (ii) suggest that the solvation effects are smaller for γTHS than for βSHS. [ABSTRACT FROM AUTHOR]

BACKGROUND: To say data is revolutionising the medical sector would be a vast understatement. The amount of medical data available today is unprecedented and has the potential to enable to date unseen forms of healthcare. To process this huge amount of data, an equally huge amount of computing power is required, which cannot be provided by regular desktop computers. These areas can be (and already are) supported by High-Performance-Computing (HPC), High-Performance Data Analytics (HPDA), and AI (together "HPC + "). OBJECTIVE: This overview article aims to show state-of-the-art examples of studies supported by the National Competence Centres (NCCs) in HPC + within the EuroCC project, employing HPC, HPDA and AI for medical applications. METHOD: The included studies on different applications of HPC in the medical sector were sourced from the National Competence Centres in HPC and compiled into an overview article. Methods include the application of HPC + for medical image processing, high-performance medical and pharmaceutical data analytics, an application for pediatric dosimetry, and a cloud-based HPC platform to support systemic pulmonary shunting procedures. RESULTS: This article showcases state-of-the-art applications and large-scale data analytics in the medical sector employing HPC + within surgery, medical image processing in diagnostics, nutritional support of patients in hospitals, treating congenital heart diseases in children, and within basic research. CONCLUSION: HPC + support scientific fields from research to industrial applications in the medical area, enabling researchers to run faster and more complex calculations, simulations and data analyses for the direct benefit of patients, doctors, clinicians and as an accelerator for medical research. [ABSTRACT FROM AUTHOR]

Electrochemically switched 2nd order non‐linear optical responses have been demonstrated for the first time in polyoxometalates (POMs), with an arylimido‐derivative showing a leading combination of high on/off contrast (94 %), high visible transparency, and cyclability. Spectro‐electrochemical and TD‐DFT studies indicate that the switch‐off results from weakened charge transfer (CT) character of the electronic transitions in the reduced state. This represents the first study of an imido‐POM reduced state, and demonstrates the potential of POM hybrids as electrochemically activated molecular switches. [ABSTRACT FROM AUTHOR]

Electrochemically switched 2nd order non‐linear optical responses have been demonstrated for the first time in polyoxometalates (POMs), with an arylimido‐derivative showing a leading combination of high on/off contrast (94 %), high visible transparency, and cyclability. Spectro‐electrochemical and TD‐DFT studies indicate that the switch‐off results from weakened charge transfer (CT) character of the electronic transitions in the reduced state. This represents the first study of an imido‐POM reduced state, and demonstrates the potential of POM hybrids as electrochemically activated molecular switches. [ABSTRACT FROM AUTHOR]