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Vincenzo Barone

Publications and source records attributed to Vincenzo Barone.

At least 19 recordsLinked to original sources
arXiv2026

SONIC: Symmetry-Oriented Non-redundant Internal Coordinates

Internal coordinates are the natural language of molecular structure, but automatic non-redundant constructions remain difficult for fused rings, high coordination, molecular symmetry, and weakly bound fragments. We present SONIC (Symmetry-Oriented Non-redundant Internal Coordinates), implemented in SMITH, as a deterministic construction of localized, symmetry-adapted generalized internal coordinates. SMITH accepts a frozen molecular state, supplied topology or primitives, or Cartesian input through a revision-pinned standalone perception kernel. It classifies ordinary primitives, adds chemically typed special and composite families, protects ring and fragment coordinates, and performs block-local rank reduction using analytic Wilson B rows. Local pseudosymmetry orders center, ring, and bond domains, while exact molecular point-group projection is applied within homogeneous blocks. The output is a frozen coordinate contract with human-readable decompositions, symmetry and rank diagnostics, analytic first derivatives, and optional Gaussian 16 serialization. Optimization, internal-to-Cartesian realization, force fields, and higher-order Hessian transformations remain downstream responsibilities. Validation covers acyclic, fused, bridged, high-coordinate, non-covalent, and eta3 metal-complex cases, including rotation/permutation invariance, Python/Fortran checks, and independent GIC evaluation.

physics.chem-ph↗
arXiv2022

Gliding on ice in search of accurate and cost-effective computational methods for astrochemistry on grains: the puzzling case of the HCN isomerization

The isomerization of hydrogen cyanide to hydrogen isocyanide on icy grain surfaces is investigated by an accurate composite method (jun-Cheap) rooted in the coupled cluster ansatz and by density functional approaches. After benchmarking density functional predictions of both geometries and reaction energies against jun-Cheap results for the relatively small model system HCN -- (H2O)2 the best performing DFT methods are selected. A large cluster containing 20 water molecules is then employed within a QM/QM$'$ approach to include a realistic environment mimicking the surface of icy grains. Our results indicate that four water molecules are directly involved in a proton relay mechanism, which strongly reduces the activation energy with respect to the direct hydrogen transfer occurring in the isolated molecule. Further extension of the size of the cluster up to 192 water molecules in the framework of a three-layer QM/QM'/MM model has a negligible effect on the energy barrier ruling the isomerization. Computation of reaction rates by transition state theory indicates that on icy surfaces the isomerization of HNC to HCN could occur quite easily even at low temperatures thanks to the reduced activation energy that can be effectively overcome by tunneling.

physics.chem-ph↗
arXiv2022

Precursors of the RNA-world in space: Detection of ($Z$)-1,2-ethenediol in the interstellar medium, a key intermediate in sugar formation

We present the first detection of ($Z$)-1,2-ethenediol, (CHOH)$_2$, the enol form of glycolaldehyde, in the interstellar medium towards the G+0.693-0.027 molecular cloud located in the Galactic Center. We have derived a column density of (1.8$\pm$0.1)$\times$10$^{13}$ cm$^{-2}$, which translates into a molecular abundance with respect to molecular hydrogen of 1.3$\times$10$^{-10}$. The abundance ratio between glycolaldehyde and ($Z$)-1,2-ethenediol is $\sim$5.2. We discuss several viable formation routes through chemical reactions from precursors such as HCO, H$_2$CO, CHOH or CH$_2$CHOH. We also propose that this species might be an important precursor in the formation of glyceraldehyde (HOCH$_2$CHOHCHO) in the interstellar medium through combination with the hydroxymethylene (CHOH) radical.

astro-ph.GA↗
arXiv2021

The junChS and junChS-F12 models: parameter-free efficient yet accurate composite schemes for energies and structures of non-covalent complexes

A recently developed model chemistry (denoted as junChS [Alessandrini et al J. Chem. Theory Comput. 2020, 16, 988-1006]) has been extended to the employment of explicitly-correlated (F12) methods. This led us to propose a family of effective, reliable and parameter-free schemes for the computation of accurate interaction energies of molecular complexes ruled by non-covalent interactions. A thorough benchmark based on a wide range of interactions showed that the so-called junChS-F12 model, which employs cost-effective revDSD-PBEP86-D3(BJ) reference geometries, has an improved performance with respect to its conventional counterpart and outperforms well-known model chemistries. Without employing any empirical parameter and at an affordable computational cost, junChS-F12 reaches sub-chemical accuracy. Accurate characterizations of molecular complexes are usually limited to energetics. To take a step forward, the conventional and F12 composite schemes developed for interaction energies have been extended to structural determinations. A benchmark study demonstrated that the most effective option is to add MP2-F12 core-valence correlation corrections to fc-CCSD(T)-F12/jun-cc-pVTZ geometries without the need of recovering the basis set superposition error and the extrapolation to the complete basis set.

physics.chem-ph↗
arXiv2021

Formation of phosphorus monoxide (PO) in the interstellar medium: insights from quantum-chemical and kinetic calculations

In recent years, phosphorus monoxide (PO) -- an important molecule for prebiotic chemistry -- has been detected in star-forming regions and in the comet 67P/Churyumov-Gerasimenko. These studies have revealed that, in the interstellar medium, PO is systematically the most abundant P-bearing species, with abundances that are $\sim$1-3 times greater than those derived for phosphorus nitride (PN), the second most abundant P-containing molecule. The reason why PO is more abundant than PN remains still unclear. Experimental studies with phosphorus in the gas phase are not available, probably because of the difficulties in dealing with its compounds. Therefore, the reactivity of atomic phosphorus needs to be investigated using reliable computational tools. To this end, state-of-the-art quantum-chemical computations have been employed to evaluate accurate reaction rates and branching ratios for the P + OH $\rightarrow$ PO + H and P + H$_2$O $\rightarrow$ PO + H$_2$ reactions in the framework of a master equation approach based on ab-initio transition state theory. The hypothesis that OH and H${_2}$O can be potential oxidizing agents of atomic phosphorus is based on the ubiquitous presence of H${_2}$O in the ISM. Its destruction then produces OH, which is another very abundant species. While the reaction of atomic phosphorus in its gound state with water is not a relevant source of PO because of emerged energy barriers, the P + OH reaction represents an important formation route of PO in the interstellar medium. Our kinetic results show that this reaction follow an Arrhenius behavior, and thus its rate coefficients alpha=2.28$\times$10$^{-10}$ cm${^3}$ molecule$^{-1}$ s$^{-1}$, beta=0.16 and gamma=0.37 K increase by increasing the temperature.

astro-ph.GA↗
arXiv2021

Development and validation of a parameter-free model chemistry for the computation of reliable reaction rates

A recently developed model chemistry (jun-Cheap) has been slightly modified and proposed as an effective, reliable and parameter-free scheme for the computation of accurate reaction rates with special reference to astrochemical and atmospheric processes. Benchmarks with different sets of state-of-the-art energy barriers spanning a wide range of values show that, in the absence of strong multi-reference contributions, the proposed model outperforms the most well-known model chemistries, reaching a sub-chemical accuracy without any empirical parameter and with affordable computer times. Some test cases show that geometries, energy barriers, zero point energies and thermal contributions computed at this level can be used in the framework of the master equation approach based on ab-initio transition state theory (AITSTME) for obtaining accurate reaction rates.

physics.chem-ph↗
arXiv2020

Methanimine as a key precursor of imines in the interstellar medium: the case of propargylimine

A gas-phase formation route is proposed for the recently detected propargylimine molecule. In analogy to other imines, such as cyanomethanimine, the addition of a reactive radical (C$_2$H in the present case) to methanimine (CH$_2$NH}) leads to reaction channels open also in the harsh conditions of the interstellar medium. Three possible isomers can be formed in the C$H_2$NH + C$_2$H reaction: Z- and E-propargylimine (Z-,E-PGIM) as well as N-ethynyl-methanimine (N-EMIM). For both PGIM species, the computed global rate coefficient is nearly constant in the 20-300 K temperature range, and of the order of 2-3 $\times$ 10$^{-10}$ cm$^3$ molecule$^{-1}$ s$^{-1}$, while that for N-EMIM is about two orders of magnitude smaller. Assuming equal destruction rates for the two isomers, these results imply an abundance ratio for PGIM of [Z]/[E] $\sim$ 1.5, which is only slightly underestimated with respect to the observational datum.

astro-ph.GA↗
arXiv2020

The Role of State-of-the-Art Quantum-Chemical Calculations in Astrochemistry: Formation Route and Spectroscopy of Ethanimine as a Paradigmatic Case

The gas-phase formation and spectroscopic characteristics of ethanimine have been re-investigated as a paradigmatic case illustrating the accuracy of state-of-the-art quantum-chemical (QC) methodologies in the field of astrochemistry. According to our computations, the reaction between the amidogen, NH, and ethyl, C$_2$H$_5$, radicals is very fast, close to the gas-kinetics limit. Although the main reaction channel under conditions typical of the interstellar medium leads to methanimine and the methyl radical, the predicted amount of the two E,Z stereoisomers of ethanimine is around 10%. State-of-the-art QC and kinetic models lead to a [E-CH$_3$CHNH]/[Z-CH$_3$CHNH] ratio of ca. 1.4, slightly higher than the previous computations, but still far from the value determined from astronomical observations (ca. 3). An accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the E and Z isomers of ethanimine combined with millimeter-wave measurements up to 300 GHz, allows for predicting the rotational spectrum of both isomers up to 500 GHz, thus opening the way toward new astronomical observations.

astro-ph.GA↗
arXiv2020

State-of-the-Art Quantum Chemistry Meets Variable Reaction Coordinate Transition State Theory to Solve the Puzzling Case of the H2S + Cl System

The atmospheric reaction of H$_2$S with Cl has been reinvestigated to check if, as previously suggested, only explicit dynamical computations can lead to an accurate evaluation of the reaction rate because of strong recrossing effects and the breakdown of the variational extension of transition state theory. For this reason, the corresponding potential energy surface has been thoroughly investigated, thus leading to an accurate characterization of all stationary points, whose energetics has been computed at the state of the art. To this end, coupled-cluster theory including up to quadruple excitations has been employed, together with the extrapolation to the complete basis set limit and also incorporating core-valence correlation, spin-orbit, and scalar relativistic effects as well as diagonal Born-Oppenheimer corrections. This highly accurate composite scheme has also been paralleled by less expensive yet promising computational approaches. Moving to kinetics, variational transition state theory and its variable reaction coordinate extension for barrierless steps have been exploited, thus obtaining a reaction rate constant (8.16 x 10$^{-11}$ cm$^3$ molecule$^{-1}$ s$^{-1}$ at 300 K and 1 atm) in remarkable agreement with the experimental counterpart. Therefore, contrary to previous claims, there is no need to invoke any failure of the transition state theory, provided that sufficiently accurate quantum-chemical computations are performed. The investigation of the puzzling case of the H$_2$S + Cl system allowed us to present a robust approach for disclosing the thermochemistry and kinetics of reactions of atmospheric and astrophysical interest.

physics.chem-ph↗
arXiv2020

A Systematic Study on the Absorption Features of Interstellar Ices in Presence of Impurities

Spectroscopic studies play a key role in the identification and analysis of interstellar ices and their structure. Some molecules have been identified within the interstellar ices either as pure, mixed, or even as layered structures. Absorption band features of water ice can significantly change with the presence of different types of impurities (CO, CO2, CH3OH, H2CO, etc.). In this work, we carried out a theoretical investigation to understand the behavior of water band frequency, and strength in the presence of impurities. The computational study has been supported and complemented by some infrared spectroscopy experiments aimed at verifying the effect of HCOOH, NH3 , and CH3 OH on the band profiles of pure H2O ice. Specifically, we explored the effect on the band strength of libration, bending, bulk stretching, and free-OH stretching modes. Computed band strength profiles have been compared with our new and existing experimental results, thus pointing out that vibrational modes of H2O and their intensities can change considerably in the presence of impurities at different concentrations. In most cases, the bulk stretching mode is the most affected vibration, while the bending is the least affected mode. HCOOH was found to have a strong influence on the libration, bending, and bulk stretching band profiles. In the case of NH3, the free-OH stretching band disappears when the impurity concentration becomes 50%. This work will ultimately aid a correct interpretation of future detailed spaceborne observations of interstellar ices by means of the upcoming JWST mission.

astro-ph.GA↗
arXiv2019

Optimization of highly excited matrix product states with an application to vibrational spectroscopy

Configuration-interaction-type calculations on electronic and vibrational structure are often the method of choice for the reliable approximation of many-particle wave functions and energies. The exponential scaling, however, limits their application range. An efficient approximation to the full configuration interaction solution can be obtained with the density matrix renormalization group (DMRG) algorithm without a restriction to a predefined excitation level. In a standard DMRG implementation, however, excited states are calculated with a ground-state optimization in the space orthogonal to all lower lying wave function solutions. A trivial parallelization is therefore not possible and the calculation of highly excited states becomes prohibitively expensive, especially in regions with a high density of states. Here, we introduce two variants of the density matrix renormalization group algorithm that allow us to target directly specific energy regions and therefore highly excited states. The first one, based on shift-and-invert techniques, is particularly efficient for low-lying states, but is not stable in regions with a high density of states. The second one, based on the folded auxiliary operator, is less efficient, but more accurate in targeting high-energy states. We apply the algorithm to the solution of the nuclear Schroedinger equation, but emphasize that it can be applied to the diagonalization of general Hamiltonians as well, such as the electronic Coulomb Hamiltonian to address X-ray spectra. In combination with several root-homing algorithms and a stochastic sampling of the determinant space, excited states of interest can be adequately tracked and analyzed during the optimization. We demonstrate that we can accurately calculate prominent spectral features of large molecules such as the sarcosyn-glycine dipeptide.

physics.comp-ph↗
arXiv2018

On the composition of an arbitrary collection of $SU(2)$ spins: An Enumerative Combinatoric Approach

The whole enterprise of spin compositions can be recast as simple enumerative combinatoric problems. We show here that enumerative combinatorics (EC)\citep{book:Stanley-2011} is a natural setting for spin composition, and easily leads to very general analytic formulae -- many of which hitherto not present in the literature. Based on it, we propose three general methods for computing spin multiplicities; namely, 1) the multi-restricted composition, 2) the generalized binomial and 3) the generating function methods. Symmetric and anti-symmetric compositions of $SU(2)$ spins are also discussed, using generating functions. Of particular importance is the observation that while the common Clebsch-Gordan decomposition (CGD) -- which considers the spins as distinguishable -- is related to integer compositions, the symmetric and anti-symmetric compositions (where one considers the spins as indistinguishable) are obtained considering integer partitions. The integers in question here are none other but the occupation numbers of the Holstein-Primakoff bosons. \par The pervasiveness of $q-$analogues in our approach is a testament to the fundamental role they play in spin compositions. In the appendix, some new results in the power series representation of Gaussian polynomials (or $q-$binomial coefficients) -- relevant to symmetric and antisymmetric compositions -- are presented.

math-ph↗
arXiv2017

The genealogical tree of ethanol: gas-phase formation of glycolaldehyde, acetic acid and formic acid

Despite the harsh conditions of the interstellar medium, chemistry thrives in it, especially in star forming regions where several interstellar complex organic molecules (iCOMs) have been detected. Yet, how these species are synthesised is a mystery. The majority of current models claim that this happens on interstellar grain surfaces. Nevertheless, evidence is mounting that neutral gas-phase chemistry plays an important role. In this article, we propose a new scheme for the gas-phase synthesis of glycolaldehyde, a species with a prebiotic potential and for which no gas-phase formation route was previously known. In the proposed scheme, the ancestor is ethanol and the glycolaldehyde sister species are acetic acid (another iCOM with unknown gas-phase formation routes) and formic acid. For the reactions of the new scheme with no available data, we have performed electronic structure and kinetics calculations deriving rate coefficients and branching ratios. Furthermore, after a careful review of the chemistry literature, we revised the available chemical networks, adding and correcting several reactions related to glycolaldehyde, acetic acid and formic acid. The new chemical network has been used in an astrochemical model to predict the abundance of glycolaldehyde, acetic acid and formic acid. The predicted abundance of glycolaldehyde depends on the ethanol abundance in the gas phase and is in excellent agreement with the measured one in hot corinos and shock sites. Our new model overpredicts the abundance of acetic acid and formic acid by about a factor of ten, which might imply a yet incomplete reaction network.

astro-ph.SR↗
arXiv2017

Laboratory measurements and astronomical search for cyanomethanimine

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. 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. 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. 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 $\sim$700 GHz. So far, no C-cyanomethanimine emission has been detected toward the ASAI targets, and upper limits of the column density of $\sim$ 10$^{11}$--10$^{12}$ 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, $\leq$ 10$^{-9}$, is obtained for shocks sites. The combination of the upper limits of the abundances of C-cyanomethanimine together with accurate laboratory frequencies up to $\sim$ 700 GHz poses the basis for future higher sensitivity searches around Sun-like-star forming regions.

astro-ph.GA↗
arXiv2017

Vibrational Density Matrix Renormalization Group

Variational approaches for the calculation of vibrational wave functions and energies are a natural route to obtain highly accurate results with controllable errors. However, the unfavorable scaling and the resulting high computational cost of standard variational approaches limit their application to small molecules with only few vibrational modes. Here, we demonstrate how the density matrix renormalization group (DMRG) can be exploited to optimize vibrational wave functions (vDMRG) expressed as matrix product states. We study the convergence of these calculations with respect to the size of the local basis of each mode, the number of renormalized block states, and the number of DMRG sweeps required. We demonstrate the high accuracy achieved by vDMRG for small molecules that were intensively studied in the literature. We then proceed to show that the complete fingerprint region of the sarcosyn-glycin dipeptide can be calculated with vDMRG.

physics.chem-ph↗
arXiv2017

A direct extraction of the Sivers distributions from spin asymmetries in pion and kaon leptoproduction

We present a point-by-point determination of the Sivers distributions from hadron leptoproduction data. The method, which relies on some simple assumptions, is based on the combined analysis of proton and deuteron observables. We make use of the single-spin asymmetries measured by COMPASS in semi-inclusive deep inelastic scattering of 160 GeV muons on transversely polarized proton and deuteron targets.

hep-ph↗
arXiv2015

Extracting the transversity distributions from single-hadron and dihadron production

We present a point-by-point determination of the valence transversity distributions from two different types of processes: single-hadron production and dihadron production, both in semi-inclusive deep inelastic scattering and e+e- annihilation. The extraction is based on some simple assumptions and does not require any parametrization. The transversity distributions obtained from Collins effect in single-hadron production and from interference effects in dihadron production are found to be compatible with each other.

hep-ph↗