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The dynamics and kinetics of spin-forbidden transitions between N(2D) and N(4S) via collisions with N2 molecules are investigated using a quantum wave packet (WP) method and the semi-classical coherent switches...

Hereditary angioedema (HAE) poses a high burden of disease, being its epidemiological and clinical data heterogeneous among countries, with no recent published studies concerning Portuguese patients. Therefore, we aimed to raise awareness of HAE and to contribute to clinical knowledge. An observational, descriptive, retrospective, and cross-sectional study was performed, that included a cohort of 126 patients followed in a single Portuguese Center. We observed a high prevalence of HAE-C1-INH type II (45.2% of patients). Most HAE patients (67.4%) presented the initial manifestations of the disease before adulthood, at a mean age of 12.6 ± 8.4 years. However, we found a long delay in HAE diagnosis, especially in those without family history (mean 20.7 ± 17.3 years). Stress was the most common trigger, followed by trauma and infection. Symptoms involving different systems were increasingly reported with increased disease duration. Cutaneous symptoms (95.0%) were more frequent, followed by gastrointestinal (80.7%), and respiratory symptoms (50.4%). HAE symptoms led to abdominal surgery in 22 (17.5%) patients and induced laryngeal edema requiring intubation/tracheostomy in 8 (6.3%) patients. Most patients were under long-term prophylaxis, mainly with attenuated androgens (62.7% of patients).The correct distinction between HAE and other common causes of angioedema is critical, allowing reduction of diagnostic delay, improvement of adequate management, and ultimately improving outcomes and quality of life of HAE patients.

SiC

The initial state-selected dynamics of the N(2D) + N2(X1∑) → N2(X1∑) + N(2D) exchange reaction on its electronic ground doublet state N3(12A″) potential energy surface (PES) has been studied here by time-dependent quantum mechanics (TDQM) and quasi-classical trajectory (QCT) methods. Dynamical attributes such as total reaction probabilities, state-selected integral cross sections, and initial state-selected rate constants have been calculated. The presence of metastable quasi-bound complexes in the collision process is confirmed by substantial oscillatory structures in the reaction probability curves. Also, rotational excitations of reagent N2 on the reactivity have been examined by calculating the probabilities for the two-body rotational angular momentum up to j = 10. We conclude that the reagent rotational excitation increases the reactivity. The TDQM results are compared with QCT results.

We have carried out quantum dynamics calculations for the O + OH → H + O2 reaction on the CHIPR [A. J. C. Varandas, J. Chem. Phys., 2013, 138, 134117] potential energy surface (PES) for ground state HO2 using the fully coupled 3D time-dependent wavepacket formalism [S. Adhikari and A. J. C. Varandas, Comput. Phys. Commun., 2013, 184, 270] in hyperspherical coordinates. Reaction probabilities for J > 0 are calculated for different initial rotational states of the OH radical (v = 0; j = 0, 1). State-to-state as well as total integral cross sections and rate-coefficients are evaluated and compared with previous theoretical calculations and available experimental studies. Using the rate constant for the forward (hereinafter considered to be H + O2 → O + OH) and backward (O + OH → H + O2) reactions of this reactive system, the equilibrium constant of the reversible process [H + O2 ⇌ O + OH] is calculated as a function of temperature and compared with previous experimental measurements.

Cost-effectiveness and accuracy are two basic pillars in electronic structure calculations. While cost-effectiveness enhances applicability, high accuracy is sustained when employing advanced computational tools. With the gold standard method of ab initio quantum chemistry at the focal point, canonical CCSD(T) and modern explicitly correlated CCSD(T)-F12 calculations are employed hand in hand to develop accurate hybrid post-CBS extrapolation schemes, which are validated using popular training sets involving a total of 130 molecules. By using raw valence-only calculations at CCSD(T)/VDZ and CCSD(T)/VQZ-F12 levels of theory, the novel scheme leads to the prediction of absolute energies that differ on average (−0.170 ± 0.224) kcal mol−1 from the highest affordable CCSD(T)-F12b/V(Q,5)Z-F12 extrapolations, but only (−0.048 ± 0.228) kcal mol−1 from the post-CBS extrapolated values based on CBS(D,T), CBS(D,Q) and CBS(T,Q) energies. From the cost-effectiveness standpoint, the approach is a kind of pseudo one-point extrapolation scheme since its cost is basically that of the highest-rung raw energy where it is based. Variants that imply no additional cost are also discussed, emerging h-pCBS(dt,dq)ab as the most effective. The approach can also be used with PNO-based local correlation methods that gained popularity due to allowing coupled-cluster calculations even for large molecules at reduced computational cost, namely local PNO-CCSD(T) and PNO-CCSD(T)-F12b. To gauge the approach performance, both the hydrogen molecule and the O–C2H5 torsion path of ethyl-methyl-ether, an extra molecule here considered with presupposed existence in astrophysical objects, are also studied. Additionally, the nonbonding interactions in the A24 test set are revisited per se. The results show that the title approach may be useful in high-accuracy quantum chemistry, with further improvements requiring the inclusion of contributions beyond the theory here employed such as the ones due to relativistic and nonadiabatic effects.

The stability of four fermionic particles with unit charge, of which two are positively and two negatively charged, is discussed. Except for using the simplest approximation of a single Gaussian orbital per particle, the problem is exactly solved variationally by varying the masses to simulate molecular di-hydrogen, mono-muonated di-hydrogen, and di-muonated di-hydrogen. We illustrate the celebrated Born–Oppenheimer approximation 2 years after the occasion of its 90th anniversary. It is suggested that this method is valid only for di-hydrogen.

A global potential energy surface for the lowest quartet state of HN2 is reported for the first time from accurate multi-reference ab initio calculations extrapolated to the complete basis set limit using the double many-body expansion method. All its stationary points are characterized, with the lowest quartet of HN2 predicted to have a bent global minimum 36 kcal mol-1 below the N(4S)+NH(X 3Σ−) asymptote, from which it is barrierlessly achievable. The entire set of calculated ab initio points has been fitted for energies up to 1000 kcal mol-1 above the global minimum with a rmsd of 0.89 kcal mol-1, a gap comprising all identified stationary points. Special care is taken in modeling the involved long-range for ces, and cusps caused by crossing seams. The novel PES will prompt for the calculation of rate constants for several unexplored reactions that are relevant for combustion, plasma and atmospheric chemistry.

We have carried out quantum dynamics calculations for the O + OH → H + O

The initial state-selected dynamics of the N(

Cost-effectiveness and accuracy are two basic pillars in electronic structure calculations. While cost-effectiveness enhances applicability, high accuracy is sustained when employing advanced computational tools. With the gold standard method of ab initio quantum chemistry at the focal point, canonical CCSD(T) and modern explicitly correlated CCSD(T)-F12 calculations are employed hand in hand to develop accurate hybrid post-CBS extrapolation schemes, which are validated using popular training sets involving a total of 130 molecules. By using raw valence-only calculations at CCSD(T)/VDZ and CCSD(T)/VQZ-F12 levels of theory, the novel scheme leads to the prediction of absolute energies that differ on average (-0.170 ± 0.224) kcal mol-1 from the highest affordable CCSD(T)-F12b/V(Q,5)Z-F12 extrapolations, but only (-0.048 ± 0.228) kcal mol-1 from the post-CBS extrapolated values based on CBS(D,T), CBS(D,Q) and CBS(T,Q) energies. From the cost-effectiveness standpoint, the approach is a kind of pseudo one-point extrapolation scheme since its cost is basically that of the highest-rung raw energy where it is based. Variants that imply no additional cost are also discussed, emerging h-pCBS(dt,dq)ab as the most effective. The approach can also be used with PNO-based local correlation methods that gained popularity due to allowing coupled-cluster calculations even for large molecules at reduced computational cost, namely local PNO-CCSD(T) and PNO-CCSD(T)-F12b. To gauge the approach performance, both the hydrogen molecule and the O-C2H5 torsion path of ethyl-methyl-ether, an extra molecule here considered with presupposed existence in astrophysical objects, are also studied. Additionally, the nonbonding interactions in the A24 test set are revisited per se. The results show that the title approach may be useful in high-accuracy quantum chemistry, with further improvements requiring the inclusion of contributions beyond the theory here employed such as the ones due to relativistic and nonadiabatic effects.

We assess benchmark correlation energies for 130 systems in test sets A24 and TS-106 both with the canonical CCSD(T) and explicitly correlated CCSD(T)-F12 methods. Aiming at enhanced accuracy, the calculated raw energies from both sets are CBS extrapolated to the complete basis set (CBS) limit and subsequently post-CBS extrapolated. Attention is focused at total energies, since their accuracy reflects on that of the interaction energies. Using up to triple-ζ basis sets for CBS and an additional quadruple-ζ for post-CBS, the mean and standard unsigned deviations with canonical CCSD(T) theory are 0.257 ± 0.25 kcal mol−1, while the corresponding values for CCSD(T)-F12 in its F12a and F12b variants with specialized basis sets up to VQZ-F12 are 0.170 ± 0.13 kcal mol−1 and 0.048 ± 0.04 kcal mol−1. Although these show gains at post-CBS level that vary from 0.08 to 0.20 kcal mol−1 relative to their CCSD(T)/VXZ analogues, the convergence is somewhat less clear when extending the basis up to V5Z-F12, the highest-rung available: 0.220 ± 0.17 kcal mol−1 and 0.142 ± 0.08 kcal mol−1, in the same order. An explanation for the up to one order of magnitude smaller deviations in energy differences is detailed. Based on energy differences involving basis set pairs employed for extrapolating to the CBS limit, a convergence diagnostic is also suggested. Arising from irregularities in the basis set that directly correlate with non-dynamical correlation, the new diagnostic may complement popular ones that feature other aspects of correlation.

Quasiclassical trajectories have been run for N 2 A 3 Σ u + + H 2 S collisions allowing for electronic transitions through surface hopping. An accurate multi-sheeted representation of the HN2 potential energy surface has been employed. For the rate constant at room temperature, we obtain 9.85 ± 0.16 × 10 - 10 cm 3 s - 1 , a value fivefold larger than the recommended experimental one. Unprecedently, we investigate the temperature dependence of the rate constant, and obtained an essentially flat Arrehenius plot. We estimate that the NH yield is at least one order of magnitude lower than the experimental upper limit.

The predicted rate constants for C + NO and O + CN collisions in three potential energy surfaces (PESs) for the 2A' state of the CNO molecule are compared using quasiclassical trajectories. Different temperature dependencies are obtained for the C + NO reaction, which are explained in terms of the long-range properties of the PESs. Recommended values and mechanistic details are also reported. For O + CN collisions, a better agreement between the theoretical results is found, except for temperatures below 100 K.

We report the first global ab initio-based potential energy surface (PES) for ground-state triplet C3(3A′) based on accurate energies extrapolated to the complete basis set (CBS) limit, and using t...

An analytical potential energy function for the title ion based on the combined hyperbolic inverse power representation (CHIPR) method and its characteristics are discussed at length in the present work. The curves of two diatomic ions, O2+ and OH+, are also obtained within the same approach. The model PES so obtained exhibits extraordinary flexibility in describing with subchemical accuracy even the weak topological features near the higher energy regions. Thus, structural properties predicted by the model may help spectroscopists who want to compare their experimental values with the ones from theory. The relaxed PESs in various coordinates have been calculated by relaxing the O2 bond distance using the present model, thus throwing light on all the possible isomers and their interconversions. The latest estimates of IR frequencies for three vibrational modes have been compared with the computed frequencies using the present model, and the agreement seems encouraging.

The previously reported potential energy surfaces (PESs) of ground-state singlet C3 and triplet C4 are here utilized as input for the construction of approximate cluster expansions for larger Cκ (κ = 5-10) species. Relying primarily on the double many-body expansion (DMBE) approach, global potentials are obtained by summing the total interaction energies of all atomic subclusters up to four-body terms. The notable capability of the final forms in predicting good estimates of the linear global minima and their thermochemical/structural properties may provide important insights into the structure-determining nature of the (2 + 3 + 4) terms. The main difficulties and virtues in assessing Cκ's via DMBE theory are analyzed and new prospects given for the construction of global reliable PESs for the target species.

A full-dimensional global potential-energy surface (PES) is first reported for ground-state doublet C3H using the combined-hyperbolic-inverse-power-representation (CHIPR) method and accurate ab initio energies extrapolated to the complete basis set limit. The PES is based on a many-body expansion-type development where the two-body and three-body energy terms are from our previously reported analytic potentials for C2H(2A') and C3(1A',3A'), while the effective four-body one is calibrated using an extension of the CHIPR formalism for tetratomics. The final form is shown to accurately reproduce all known stationary structures of the PES, some of which are unreported thus far, and their interconversion pathways. Moreover, it warrants by built-in construction the appropriate permutational symmetry and describes in a physically reasonable manner all long-range features and the correct asymptotic behavior at dissociation. Exploratory quasi-classical trajectory calculations for the reaction C2 + CH → C3 + H are also performed, yielding thermalized rate coefficients for temperatures up to 4000 K.

Quantum dynamics of the H + O2→ O + OH reaction has been extensively studied on the adiabatic ground state of CHIPR [A. J. C. Varandas, J. Chem. Phys., 2013, 138, 134117] potential energy surfaces by employing a coupled 3D time-dependent wavepacket approach in hyperspherical coordinates. Calculations have been performed for all non-zero J values for various initial rotational states of the diatom [O2(v = 0, j = 1-5)]. State-to-state and total integral cross sections are calculated using fully converged reaction probabilities, where initial state selected and Boltzmann averaged thermal rate constants are also subsequently calculated. Moreover, a comparison of various reaction attributes obtained by using the fully close coupled approach with the ones obtained from the J-shifting approximation and extrapolation scheme is presented along with other theoretical results and experimental observations.

A realistic double many-body expansion potential energy surface (PES) is developed for the

Silicon monosulfide is an important silicon bearing molecule detected in circumstellar envelopes and star forming regions. Its formation and destruction routes are not well understood, partially due to the lack of a detailed knowledge on the involved reactions and their rate coefficients. In this work we have calculated and modeled the potential energy surface (PES) of the HSiS system employing highly accurate multireference electronic structure methods. After obtaining an accurate analytic representation of the PES, which includes long-range energy terms in a realistic way via the DMBE method, we have calculated rate coefficients for the Si+SH$\rightarrow$SiS+H reaction over the temperature range of 25-1000K. This reaction is predicted to be fast, with a rate coefficient of $\sim 1\times 10^{-10}\rm cm^3\, s^{-1}$ at 200K, which substantially increases for lower temperatures (the temperature dependence can be described by a modified Arrhenius equation with $\alpha=0.770\times 10^{-10}\rm cm^3\,s^{-1}$, $\beta=-0.756$ and $\gamma=9.873\, \rm K$). An astrochemical gas-grain model of a shock region similar to L1157-B1 shows that the inclusion of the Si+SH reaction increases the SiS gas-phase abundance relative to \ce{H2} from $5\times 10^{-10}$ to $1.4\times 10^{-8}$, which perfectly matches the observed abundance of $\sim 2\times 10^{-8}$., Comment: 11 pages, 7 figures. Accepted for publication in The Astrophysical Journal

The emission of carbon dioxide in large amounts is commonly believed to be the main cause of global climate changes. Development of CO2 capture processes is still a big current challenge. Some anions have been studied for the gas sequestration process due their great affinity to CO2. In this work, electronic structure calculations were performed at the MP2/aug-cc-pvtz level to compute the interaction between 20 anions and CO2. A CBS scheme, using extrapolated energies, was also employed for both gas phase and solvent calculations. The reactions between the anions and CO2 were therefore studied in four different conditions (gas phase, toluene, tetrahydrofuran and water). The trends observed for the reaction thermodynamics with the MP2 method is similar to that observed previously with the B3LYP-D3 and M06-2X functionals. The reactions in the gas phase are highly exothermic and do not involve any activation energy. The solvent effect reduces the exothermicity and induces an intrinsic activation barrier. The negative charge is dispersed in the adduct, leading to a weaker interaction in a polar solvent. Then, increasing the medium polarity, the energy difference between the adduct and the reactants decreases. We also observed a limit for solvent stabilization in the low dielectric constant range. For example, the results obtained with tetrahydrofuran are closer to those obtained with water than to those obtained with toluene. Considering both the thermodynamics of the reaction and the differential solvent effects, we were able to indicate anions derived from alkyl sulfides as the most convenient for CO2 sequestration among the set here considered.

A global potential energy surface for the lowest quartet state of HN

Following a previous work, we have assessed the feasibility of MP2/CBS(d, t) as an alternative to state-of-the-art density functionals. The effect of using augmented basis sets is here tested on the 76 barrier heights and 10 isomerization reactions previously utilized. Moreover, calculations for 20 sets of the GMTKN24 database for thermochemistry, kinetics, and noncovalent interactions have been performed. For the density functional theory calculations, M06-2X and B3LYP-D3 functionals are utilized as two representative functionals, while MP2 and CCSD(T) methods are employed as the ab initio counterparts. The results show that MP2 calculations perform similarly to the ones obtained with M06-2X insofar as accuracy and computational cost are concerned. For all methods, the use of augmented basis sets yields enhanced results for anionic systems when compared with the ones from non-augmented bases. Otherwise, the basis-set change effect is found to be minimal. It is therefore concluded that the use of large basis sets is unjustified when facing the increase in computational cost.

We have carried out a quasiclassical trajectory study of the O + NO(v) energy transfer process using DMBE potential energy surfaces for the ground-states of the 2A′ and 2A″ manifolds. State-to-state vibrational relaxation rate constants have been computed over the temperature range 298 and 3000 K and initial vibrational states between v = 1 and 9. The momentum-Gaussian binning approach has been employed to calculate the probability of the vibrational transitions. A comparison of the calculated state-to-state rate coefficients with the results from experimental studies and previous theoretical calculations shows the relevance of the 1 2A″ potential energy surface to the title vibrational relaxation process.

The multiple energy switching scheme [J. Chem. Phys. 119 (2003) 2596] has been used to improve the double many-body expansion (DMBE II) potential energy surface of C 3 near its linear global minima by morphing it with an accurate Taylor-series expansion [J. Chem. Phys. 144 (2016) 044307]. The final ES form attains the accuracy of the local form in reproducing the rovibrational spectrum of C 3 while keeping unaltered all key attributes of the original DMBE II, namely conical intersection seams and dissociative channels. The ES form is therefore commended for adiabatic spectroscopic and reaction dynamics studies.

Because the one-electron basis set limit is difficult to reach in correlated post-Hartree–Fock ab initio calculations, the low-cost route of using methods that extrapolate to the estimated basis set limit attracts immediate interest. The situation is somewhat more satisfactory at the Hartree–Fock level because numerical calculation of the energy is often affordable at nearly converged basis set levels. Still, extrapolation schemes for the Hartree–Fock energy are addressed here, although the focus is on the more slowly convergent and computationally demanding correlation energy. Because they are frequently based on the gold-standard coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)], correlated calculations are often affordable only with the smallest basis sets, and hence single-level extrapolations from one raw energy could attain maximum usefulness. This possibility is examined. Whenever possible, this review uses raw data from second-order Møller–Plesset perturbation theory, as well as CCSD, CCSD(T), and multireference configuration interaction methods. Inescapably, the emphasis is on work done by the author's research group. Certain issues in need of further research or review are pinpointed.

A potential energy surface is reported at the complete basis set limit for the ground electronic state of HO 2 + via a four dimensional interpolation in relaxed hyperspherical coordinates. The dissociated products OH + and O 2 + have also been studied at the complete basis set level and subsequently analytically modelled. In the case of O 2 + , the vibrational states predicted from the model potential have also been directly included in the fit. The potential form so obtained matches the RKR levels with a root mean square deviation below 1 cm - 1 . Spin orbit + relativistic effects have also been taken into account for the O 2 + ion.

We perform quantum dynamics calculations for the reaction H + O2 → O + OH on the ground-state potential energy surfaces CHIPR [Varandas, J. Chem. Phys., 2013, 138, 134117] and DMBE IV [Pastrana et al., J. Phys. Chem. 1990, 94, 8073] using a three-dimensional time-dependent wave packet formalism based on hyperspherical coordinates. Initial rovibrational state [O2(v = 0–4, j = 1–5)] dependent reaction probabilities are calculated for the case J = 0. The J-shifting scheme is employed to estimate initial state selected integral cross-sections as well as thermal rate coefficients, which is verified using a realistic extrapolation scheme. The calculated total and state-to-state rate coefficients are compared with the findings of recent experimental studies and previous theoretical calculations.

A new single-sheeted DMBE potential energy surface for ground-state C3 is reported. The novel analytical form accurately describes the three symmetry-equivalent C2v disjoint seams, in addition to the symmetry-required D3h one, over the entire configuration space. The present formalism warrants by built-in construction the confluence of the above crossings, and the rotation-in-plane of the C2v seams when the perimeter of the molecule fluctuates. Up to 1050 ab initio energies have been employed in the calibration procedure, of which 421 map the loci of intersection. The calculated energies have been scaled to account for the incompleteness of the basis set and truncation of the MRCI expansion, and fitted analytically with chemical accuracy. The novel form is shown to accurately mimic the region defined by the 4 conical intersections, while exhibiting similar attributes to the previously reported one [J. Chem. Phys., 2015, 143, 074302] at the regions of configuration space away from the crossing seams. Despite being mainly addressed to C3, the present approach should be applicable to adiabatic PESs of any X3 system experiencing similar topological attributes, in particular the small-linear-parameter Jahn–Teller molecules.

Despite its paradigmatic role in early molecular beam experiments and theoretical molecular reaction dynamics, an attempt is made in the present work to elucidate basic aspects of the title reaction. Both thermal rate constants and its rotation specificity are studied using two recently reported ab initio potential energy surfaces by running quasiclassical trajectories. Some inconsistencies in previous studies are pinpointed, but the results show that they do not alter significantly the agreement between experiment and theory, thus suggesting that further work at both levels is necessary for a more complete understanding.

To assess the title issue, 38 hydrogen transfer barrier heights and 38 non-hydrogen transfer barrier heights/isomerizations extracted from extensive databases have been considered, in addition to 4 2 p-isomerization reactions and 6 others for large organic molecules. All Kohn-Sham DFT calculations have employed the popular M06-2X functional, whereas the correlated molecular orbital (MO)-based ones are from single-reference MP2 and CCSD(T) methods. They have all utilized the same basis sets, with raw MO energies subsequently extrapolated to the complete basis set limit without additional cost. MP2 calculations are found to be as cost-effective as DFT ones and often slightly more, while showing a satisfactory accuracy when compared with the reference data. Although the focus is on barrier heights, the results may bear broader implications, in that one may see successes and difficulties of DFT when compared with traditional MO theories for the same data.