Accurate thermochemistry at affordable cost by means of an improved version of the JunChS-F12 model chemistry.

The junChS-F12 composite method has been improved by means of the latest implementation of the CCSD(F12*)(T+) ansatz and validated for the thermochemistry of molecules containing atoms of the first three rows of the periodic table. A thorough benchmark showed that this model, in conjunction with cost-effective revDSD-PBEP86-D3(BJ) reference geometries, offers an optimal compromise between accuracy and computational cost. If improved geometries are sought, the most effective option is to add MP2-F12 core-valence correlation corrections to CCSD(T)-F12b/jun-cc-pVTZ geometries without the need of performing any extrapolation to the complete basis set limit. In the same vein, CCSD(T)-F12b/jun-cc-pVTZ harmonic frequencies are remarkably accurate without any additional contribution. Pilot applications to noncovalent intermolecular interactions, conformational landscapes, and tautomeric equilibria confirm the effectiveness and reliability of the model.

Bringing Machine-Learning Enhanced Quantum Chemistry and Microwave Spectroscopy to Conformational Landscape Exploration: the Paradigmatic Case of 4-Fluoro-Threonine.

A combined experimental and theoretical study has been carried out on 4-fluoro-threonine, the only naturally occurring fluorinated amino acid. Fluorination of the methyl group significantly increases the conformational complexity with respect to the parent amino acid threonine. The conformational landscape has been characterized in great detail, with special attention given to the inter-conversion pathways between different conformers. This led to the identification of 13 stable low-energy minima. The equilibrium population of so many conformers produces a very complicated and congested rotational spectrum that could be assigned through a strategy that combines several levels of quantum chemical calculations with the principles of machine learning. Twelve conformers out of 13 could be experimentally characterized. The results obtained from the analysis of the intra-molecular interactions can be exploited to accurately model fluorine-substitution effects in biomolecules.

An improved study of HCO+ and He system: Interaction potential, collisional relaxation, and pressure broadening.

In light of its ubiquitous presence in the interstellar gas, the chemistry and reactivity of the HCO+ ion requires special attention. The availability of up-to-date collisional data between this ion and the most abundant perturbing species in the interstellar medium is a critical resource in order to derive reliable values of its molecular abundance from astronomical observations. This work intends to provide improved scattering parameters for the HCO+ and He collisional system. We have tested the accuracy of explicitly correlated coupled-cluster methods for mapping the short- and long-range multi-dimensional potential energy surface of atom-ion systems. A validation of the methodology employed for the calculation of the potential well has been obtained from the comparison with experimentally derived bound-state spectroscopic parameters. Finally, by solving the close-coupling scattering equations, we have derived the pressure broadening and shift coefficients for the first six rotational transitions of HCO+ as well as inelastic state-to-state transition rates up to j = 5 in the 5-100 K temperature interval.

An ultrafast spectroscopic and quantum mechanical investigation of multiple emissions in push-pull pyridinium derivatives bearing different electron donors.

A joint experimental and theoretical approach, involving state-of-the-art femtosecond fluorescence up-conversion measurements and quantum mechanical computations including vibronic effects, was employed to get a deep insight into the excited state dynamics of two cationic dipolar chromophores (Donor-π-Acceptor(+)) where the electron deficient portion is a N-methyl pyridinium and the electron donor a trimethoxyphenyl or a pyrene, respectively. The ultrafast spectroscopic investigation, and the time resolved area normalised emission spectra in particular, revealed a peculiar multiple emissive behaviour and allowed the distinct emitting states to be remarkably distinguished from solvation dynamics, occurring in water in a similar timescale. The two and three emissions experimentally detected for the trimethoxyphenyl and pyrene derivatives, respectively, were associated with specific local emissive minima in the potential energy surface of S1 on the ground of quantum-mechanical calculations. A low polar and planar Locally Excited (LE) state together with a highly polar and Twisted Intramolecular Charge Transfer (TICT) state is identified to be responsible for the dual emission of the trimethoxyphenyl compound. Interestingly, the more complex photobehaviour of the pyrenyl derivative was explained considering the contribution to the fluorescence coming not only from the LE and TICT states but also from a nearly Planar Intramolecular Charge Transfer (PICT) state, with both the TICT and the PICT generated from LE by progressive torsion around the quasi-single bond between the methylpyridinium and the ethene bridge. These findings point to an interconversion between rotamers for the pyrene compound taking place in its excited state against the Non-equilibrated Excited Rotamers (NEER) principle.

Nonadiabatic photodynamics of phenol on a realistic potential energy surface by a novel multilayer Gaussian MCTDH program.

We report the main features of a new implementation of the Gaussian Multi-Configuration Time-Dependent Hartree (G-MCTDH) model. The code allows effective computations of time-dependent phenomena, including calculation of vibronic spectra (in one or more electronic states), relative state populations etc., with the possibility of a multilayer formulation. We have validated the code on the diabatic surfaces recently published by Truhlar and coworkers to study the nonadiabatic photodynamics of phenol. Using an Ehrenfest-like, single-nuclear-configuration (but in a fully quantum formalism) model we calculate the optical spectrum and relative state populations of the system as a function of time.

Structural, dynamic and photophysical properties of a fluorescent dye incorporated in an amorphous hydrophobic polymer bundle.

The properties of a low molecular weight organic dye, namely 4-naphthyloxy-1-methoxy-2,2,6,6-tetramethylpiperidine, covalently bound to an apolar polyolefin were investigated by means of a multi-level approach, combining classical molecular dynamics simulations, based on purposely parameterized force fields, and quantum mechanical calculations based on density functional theory (DFT) and its time-dependent extension (TD-DFT). The structure and dynamics of the dye in its embedding medium were analyzed and discussed taking the entangling effect of the surrounding polymer into account, and also by comparing the results to those obtained for a different environment, i.e. toluene solution. Finally, the influence was investigated of long lived cages found in the polymeric embedding on photophysical properties, in terms of the slow and fast dye's internal dynamics, by comparing computed IR and UV spectra with their experimental counterparts.

A new Gaussian MCTDH program: implementation and validation on the levels of the water and glycine molecules.

We report the main features of a new general implementation of the Gaussian Multi-Configuration Time-Dependent Hartree model. The code allows effective computations of time-dependent phenomena, including calculation of vibronic spectra (in one or more electronic states), relative state populations, etc. Moreover, by expressing the Dirac-Frenkel variational principle in terms of an effective Hamiltonian, we are able to provide a new reliable estimate of the representation error. After validating the code on simple one-dimensional systems, we analyze the harmonic and anharmonic vibrational spectra of water and glycine showing that reliable and converged energy levels can be obtained with reasonable computing resources. The data obtained on water and glycine are compared with results of previous calculations using the vibrational second-order perturbation theory method. Additional features and perspectives are also shortly discussed.

Multipolar symmetric squaraines with large two-photon absorption cross-sections in the NIR region.

The two-photon absorption (TPA) properties of two extended symmetric squaraine dyes are thoroughly characterized from the experimental and quantum-chemical point of view. The two molecules are specially engineered to have a multipolar structure with increasing complexity, D-π-A-π-D and A'-π-D-π-A-π-D-π-A', respectively. The experimental TPA spectra, measured by means of the Z-scan technique in the femtoseconds regime, display considerably high values of TPA cross sections (σ(TPA)) for both molecules. In particular, the squaraine with the more extended structure shows the highest value of σ(TPA) ever reported for this class of molecules. CIS and TDDFT calculations of the one and two-photon absorption properties are carried out to clarify the origin of the observed TPA properties and fully characterize the electronic properties of these compounds. The calculations, in good agreement with the experimental data, suggest that the origin of this exceptionally high σ(TPA) can be ascribed to the presence of a peripheral A' group, that increases the density of excited states involved in the TPA process.

Standing balance of vehicle passengers: The effect of vehicle motion, task performance on post-drive balance.

BACKGROUND: Motion platforms and driving simulators have been shown to contribute to motion sickness and a short-term increase in standing postural sway. However, no studies to date have investigated how the motion of a passenger vehicle and the performance of a task during a drive on a closed test track affects post-drive standing balance. RESEARCH QUESTIONS: What are the effects of (1) a continuous, scripted drive on a closed test track, and (2) the performance of a handheld tablet-based task during the scripted drive, on post-drive standing balance? METHODS: Fifty adults (23 males, 27 females; 40.0 ± 20.6 yr) rode in the front passenger seat of a midsized sedan on a scripted drive. Participants were assigned to one of the acceleration levels (Low, Moderate) and completed both Task and No-Task test conditions, involving a visual-based task on a handheld tablet device. Before and after each scripted drive, participants completed two standing balance exercises: 1) feet tandem, eyes open, on firm support, and 2) feet together, eyes closed, on foam support. An inertial measurement unit (IMU) captured estimates of postural trunk sway. Root-mean-square (RMS) of angular position and velocity in the anteroposterior (A/P) and mediolateral (M/L) directions, and elliptical fit and path length of sway trajectory were computed. A nonparametric analysis was performed on the balance metrics. RESULTS: Exposure to a scripted drive in a vehicle affected participants' postural sway, especially after using a handheld device during the drive. M/L RMS sway velocity and path length increased for both exercises following the scripted drive with task. Additionally, M/L RMS sway increased for the more challenging balance exercise, during which participants stood with feet together on foam support with eyes closed. SIGNIFICANCE: This study is the first to explore balance following a scripted drive on a closed test track. Changes in post-drive balance introduces potential risks to vehicle passengers; concurrent performance of a task on a handheld device further increases the likelihood that post-drive balance will be negatively affected.

Excited states decay of the A-T DNA: A PCM/TD-DFT study in aqueous solution of the (9-methyl-adenine)(2).(1-methyl-thymine)(2) stacked tetramer.

By exploiting some of the most recent advances in the quantum mechanical methods, we have been able to analyze the behavior of the lowest energy excited states of A-T B-DNA using a realistic model, namely a double strand tetramer formed by two thymine-adenine stacked pairs in aqueous solution. The equilibrium structure of the lowest energy bright and dark excited states has been determined and their main properties disclosed. On this ground, our study provides a detailed atomistic picture of the excited state decay and of the emission process, and it highlights the specific roles of base stacking and pairing. While absorption involves excited states delocalized over different stacked bases, emission mainly takes place from individual monomers and it is dominated by thymine bases. We show that fast "monomer-like" excited state decay routes are operative also in the double strand. On the other hand, the long living components of the excited state population of (dA).(dT) oligomers correspond to a dark excimer produced by intermonomer charge transfer between two stacked adenine bases, whereas adenine-thymine proton transfer plays a minor role in the excited state decay.

A quantum mechanical study of TiCl3 alpha, beta and gamma crystal phases: geometry, electronic structure and magnetism.

The electronic structure of different magnetic states of alpha, beta and gamma modifications of TiCl(3) has been computed employing the density functional theory with periodic boundary conditions and localized Gaussian basis sets. The analysis of the density of the electronic states (DOS) and of the spin density makes it possible to classify these halides as Mott-Hubbard insulators, where the band gap appears a result of large on-site Coulomb interaction. For each crystalline phase, the relative stability of different magnetic states has been analyzed in terms of exchange mechanisms. The electronic population data along with the spin density maps support the assumption of a d(1) Titanium ion in a distorted octahedral crystal field, notwithstanding the not fully ionic character of TiCl(3) modifications. Dispersion forces are particularly important for this material: a classical correction (of the type f(R)/R(6)) has been added to the DFT energies and gradients, providing a good agreement with structural data.

Oxygen adsorption on beta-cristobalite polymorph: ab initio modeling and semiclassical time-dependent dynamics.

The adsorption dynamics of atomic oxygen on a model beta-cristobalite silica surface has been studied by combining ab initio electronic structure calculations with a molecular dynamics semiclassical approach. We have evaluated the interaction potential of atomic and molecular oxygen interacting with an active Si site of a model beta-cristobalite surface by performing DFT electronic structure calculations. As expected, O is strongly chemisorbed, E(b) = 5.57 eV, whereas molecular oxygen can be weakly adsorbed with a high-energy barrier to the adsorption state of approximately 2 eV. The binding energies calculated for silica clusters of different sizes have revealed the local nature of the O,O(2)-silica interaction. Semiclassical collision dynamic calculations show that O is mainly adsorbed in single-bounce collisions, with a smaller probability for adsorption via a multicollision mechanism. The probability for adsorption/desorption (reflected) collisions at the three impact energies is small but not negligible at the higher energy considered in the trajectory calculations, about P(r) = 0.2 at E(kin) = 0.8 eV. The calculations give evidence of a complex multiphonon excitation-deexcitation mechanism underlying the dynamics of stable adsorption and inelastic reflection collisions.

The gas phase anisole dimer: a combined high-resolution spectroscopy and computational study of a stacked molecular system.

The gas phase structures of anisole dimer in the ground and first singlet electronic excited states have been characterized by a combined experimental and computational study. The dimer, formed in a molecular beam, has been studied by resonance-enhanced multiphoton ionization and high-resolution laser-induced fluorescence techniques. The assignment of the rotational fine structure of the S(1) <-- S(0) electronic transition origin has provided important structural information on the parallel orientation of aromatic rings of anisole moieties. By comparison with the DFT/TD-DFT computational results, it has been possible to infer the detailed equilibrium structure of the complex. The analysis of the equilibrium structure and interaction energy confirms that the anisole dimer is stabilized by dispersive interaction in the gas phase. This is, to the best of our knowledge, the first detailed work (reporting both theoretical and high-resolution experimental data) on an isolated cluster in the pi-stacking configuration.

Intracellular Ca(2+) release channels in evolution.

Intracellular Ca(2+)-release channels (ICRCs) form a superfamily of genes that encompasses two distinct subfamilies: the inositol trisphosphate receptor and the ryanodine receptor genes, which encode the largest ion channels known today. During evolution from nematodes to man, mechanisms of gene duplication and divergence have increased the number of known ICRC genes, which have been gradually co-opted to contribute to the increasing complexity of intracellular Ca(2+) signalling required for regulation of specialised eukaryotic cell activities.

Direct role of surface oxygen vacancies in visible light emission of tin dioxide nanowires.

Tin dioxide (SnO(2)) nanowires exhibit a strong visible photoluminescence that is not observed in bulk crystalline SnO(2). To explain such effect, oxygen vacancies are often invoked without clarifying if they represent the direct origin of luminescence or if their presence triggers other radiative processes. Here we report an investigation of the nature of the visible light emission in SnO(2) nanowires, showing that both experimental and theoretical ab initio analyses support the first hypothesis. On the basis of photoluminescence quenching analysis and of first-principles calculations we show that surface bridging oxygen vacancies in SnO(2) lead to formation of occupied and empty surface bands whose transition energies are in strong agreement with luminescence features and whose luminescence activity can be switched off by surface adsorption of oxidizing molecules. Finally, we discuss how such findings may explain the decoupling between "electrical-active" and "optical-active" states in SnO(2) gas nanosensors [G. Faglia et al., Appl. Phys. Lett. 86, 011923 (2005)].

Laboratory measurements and astronomical search for cyanomethanimine.

CONTEXT: C-cyanomethanimine (HNCHCN), existing in the two Z and E isomeric forms, is a key prebiotic molecule, but, so far, only the E isomer has been detected toward the massive star-forming region. Sagittarius B2(N) using transitions in the radio wavelength domain. AIMS: With the aim of detecting HNCHCN in Sun-like-star forming regions, the laboratory investigation of its rotational spectrum has been extended to the millimeter-/submillimeter-wave (mm-/submm-) spectral window in which several unbiased spectral surveys have been already carried out. METHODS: High-resolution laboratory measurements of the rotational spectrum of C-cyanomethanimine were carried out in the 100-420 GHz range using a frequency-modulation absorption spectrometer. We then searched for the C-cyanomethanimine spectral features in the mm-wave range using the high-sensitivity and unbiased spectral surveys obtained with the IRAM 30-m antenna in the ASAI context, the earliest stages of star formation from starless to evolved Class I objects being sampled. RESULTS: For both the Z and E isomers, the spectroscopic work has led to an improved and extended knowledge of the spectroscopic parameters, thus providing accurate predictions of the rotational signatures up to ~700 GHz. So far, no C-cyanomethanimine emission has been detected toward the ASAI targets, and upper limits of the column density of ~ 1011-1012 cm-2 could only be derived. Consequently, the C-cyanomethanimine abundances have to be less than a few 10-10 for starless and hot-corinos. A less stringent constraint, ≤ 10-9, is obtained for shocks sites. CONCLUSIONS: The combination of the upper limits of the abundances of C-cyanomethanimine together with accurate laboratory frequencies up to ~ 700 GHz poses the basis for future higher sensitivity searches around Sun-like-star forming regions. For compact (typically less than 1″) and chemically enriched sources such as hot-corinos, the use of interferometers as NOEMA and ALMA in their extended configurations are clearly needed.

Assessment of Electron Propagator Methods for the Simulation of Vibrationally Resolved Valence and Core Photoionization Spectra.

The analysis of photoelectron spectra is usually facilitated by quantum mechanical simulations. Because of the recent improvement of experimental techniques, the resolution of experimental spectra is rapidly increasing, and the inclusion of vibrational effects is usually mandatory to obtain a reliable reproduction of the spectra. With the aim of defining a robust computational protocol, a general time-independent formulation to compute different kinds of vibrationally resolved electronic spectra has been generalized to also support photoelectron spectroscopy. The electronic structure data underlying the simulation are computed using different electron propagator approaches. In addition to the more standard approaches, a new and robust implementation of the second-order self-energy approximation of the electron propagator based on a transition operator reference (TOEP2) is presented. To validate our implementation, a series of molecules has been used as test cases. The result of the simulations shows that, for ultraviolet photoionization spectra, the more accurate nondiagonal approaches are needed to obtain a reliable reproduction of vertical ionization energies but that diagonal approaches are sufficient for energy gradients and pole strengths. For X-ray photoelectron spectroscopy, the TOEP2 approach, besides being more efficient, is also the most accurate in the reproduction of both vertical ionization energies and vibrationally resolved bandshapes.

Methods for Calculating Partition Functions of Molecules Involving Large Amplitude and/or Anharmonic Motions.

We present a method for calculating partition functions taking into account anharmonic contributions for systems involving both small-amplitude vibrations and hindered rotations. The Wang-Landau scheme is used in the first case, while two alternative schemes are used for hindered rotation based on imaginary time propagation and fitting of the exact energy levels as a function of quantum number. These two schemes are shown to be complementary in their ranges of applicability (in terms of the torsional rotational constant and the relevant potential). Partition functions for four different molecules are calculated and compared to simpler ones obtained using a harmonic model.

A markerless system based on smartphones and webcam for the measure of step length, width and duration on treadmill.

BACKGROUND AND OBJECTIVE: A markerless low cost prototype has been developed for the determination of some spatio-temporal parameters of human gait: step-length, step-width and cadence have been considered. Only a smartphone and a high-definition webcam have been used. METHODS: The signals obtained by the accelerometer embedded in the smartphone are used to recognize the heel strike events, while the feet positions are calculated through image processing of the webcam stream. Step length and width are computed during gait trials on a treadmill at various speeds (3, 4 and 5 km/h). RESULTS: Six subjects have been tested for a total of 504 steps. Results were compared with those obtained by a stereo-photogrammetric system (Elite, BTS Engineering). The maximum average errors were 3.7 cm (5.36%) for the right step length and 1.63 cm (15.16%) for the right step width at 5 km/h. The maximum average error for step duration was 0.02 s (1.69%) at 5 km/h for the right steps. CONCLUSION: The system is characterized by a very high level of automation that allows its use by non-expert users in non-structured environments. A low cost system able to automatically provide a reliable and repeatable evaluation of some gait events and parameters during treadmill walking, is relevant also from a clinical point of view because it allows the analysis of hundreds of steps and consequently an analysis of their variability.