In silico modelling of radiative efficiencies of anthropogenic greenhouse gases

Radiative efficiency (RE) is a climate metric adopted in international reports on climate change to quantify the greenhouse capacity of gases, and hence to guide decision-making processes and drive transitions in the production and utilization of chemicals in different application fields. Key quantities for the determination of the RE of a gas are the atmospheric irradiance profile and the infrared (IR) absorption cross section spectrum. The latter is usually measured experimentally, even though acquiring high-quality IR spectra can pose severe challenges, sometimes limiting the accuracy or the accessible spectral range. While computational quantum chemistry methods have emerged as valuable tools to simulate IR absorption properties, their application to REs estimation is still limited to the use of the double-harmonic approximation, which presents fundamental limitations. In this work, a cost-effective quantum chemical (QC) workflow including non-empirical anharmonic contributions to spectral properties and an automatic identification of conformer distribution is presented for the accurate evaluation of REs using a range of atmospheric irradiance profiles. Different levels of theory are considered, according to the current state-of-the-art, and the accuracy of the QC RE tool is demonstrated with reference to a number of representative halocarbons widely used in refrigeration, manufacturing, and pharmaceutical fields. The results show that REs can be computed with an average accuracy of 5% using double-hybrid functionals, which overshoot the widely used B3LYP method. Finally, the QC methodology is applied to determine the REs of selected halocarbons for which data is limited, or to address some contradictory results appeared in the literature for some species. The outcomes of this work demonstrate that QC anharmonic IR cross section spectra can be used to estimate REs with an accuracy on par with that of experimental measurements, hence applicable to challenging cases for providing data for policymakers as well for screening purposes when seeking new replacement compounds

Reliable gas phase reaction rates at affordable cost by means of the parameter-free junChS-F12 model chemistry

A recently developed strategy for the computation at affordable cost of reliable barrier heights ruling reactions in the gas phase (junChS, [Barone, V.; et al. J. Chem. Theory Comput. 2021, 17, 4913−4928]) has been extended to the employment of explicitly correlated (F12) methods. A thorough benchmark based on a wide range of prototypical reactions shows that the new model (referred to as junChS-F12), which employs cost-effective revDSD-PBEP86-D3(BJ) reference geometries, has an improved performance with respect to its conventional counterpart and outperforms the most well-known model chemistries without the need of any empirical parameter and at an affordable computa- tional cost. Several benchmarks show that revDSD-PBEP86- D3(BJ) structures and force fields provide zero point energies and thermal contributions, which can be confidently used, together with junChS-F12 electronic energies, for obtaining accurate reaction rates in the framework of the master equation approach based on the ab initio transition-state theory

Toward spectroscopic accuracy for the structures of large molecules at DFT cost : refinement and extension of the nano-LEGO approach

The SE100 database collecting accurate equilibrium geometries of medium size molecules obtained by the semi- experimental (SE) approach has been extended to species containing Br and I atoms. This has allowed the determination of accurate linear regressions between DFT and SE values for all the main bonds and angles involving H, B, C, N, O, F, P, S, Cl, Br, and I atoms. An improved Nano-LEGO tool has been developed, which is based on suitable hybrid and double hybrid functionals and combines in a fully coherent way the templating molecule and linear regression approaches. A number of case studies show that the new Nano LEGO tool provides geometrical parameters on par with state-of-the-art composite wave function methods, but can be routinely applied to medium- to large-size molecules. The accuracy reached for structural parameters is mirrored on rotational constants that can be predicted with an average error within 0.2%

Enthalpy of formation of carbocycles : a precise theoretical determination of experimentally imprecise measurements

Despite being one of the best-known families of organic compounds, the fact that hydrocarbons exhibit a rich variety of structures owing to branching, cyclization, and the presence of multiple bonds, means that many of their properties are yet to be determined accurately, or even at all. Among cyclic hydrocarbons, those with three- membered rings are particularly interesting because of their strain energy. In this paper, we report accurate calculations of the enthalpy of formation of three-membered carbocycles, whose experimental values have not been obtained by direct measurement of the heat of combustion. For this purpose, we used several accurate composite methods to obtain the gas-phase enthalpies of atomization and derived from them the gas-phase enthalpies of formation, using experimentally determined accurate values for the atoms. Moreover, to mini- mize the inaccuracy that can possibly arise in this procedure, we also used homodesmotic reactions designed to balance systematic errors in the geometric and electronic structure of some of the species. A careful analysis of the results shows that some of the indirectly derived values reported in the literature are far from the most accurate theoretical outcomes, and we suggest that these new ones should be adopted

Accurate Quantum Chemical Spectroscopic Characterization of Glycolic Acid: A Route Toward its Astrophysical Detection

The first step to shed light on the abiotic synthesis of biochemical building blocks, and their further evolution toward biological systems, is the detection of the relevant species in astronomical environments, including earthlike planets. To this end, the species of interest need to be accurately characterized from structural, energetic, and spectroscopic viewpoints. This task is particularly challenging when dealing with flexible systems, whose spectroscopic signature is ruled by the interplay of small- and large-amplitude motions (SAMs and LAMs, respectively) and is further tuned by the conformational equilibrium. In such instances, quantum chemical (QC) calculations represent an invaluable tool for assisting the interpretation of laboratory measurements or even observations. In the present work, the role of QC results is illustrated with reference to glycolic acid (CH2OHCOOH), a molecule involved in photosynthesis and plant respiration and a precursor of oxalate in humans, which has been detected in the Murchison meteorite but not yet in the interstellar medium or in planetary atmospheres. In particular, the equilibrium structure of the lowest-energy conformer is derived by employing the so-called semiexperimental approach. Then, accurate yet cost-effective QC calculations relying on composite post-Hartree–Fock schemes and hybrid coupled-cluster/density functional theory approaches are used to predict the structural and ro-vibrational spectroscopic properties of the different conformers within the framework of the second-order vibrational perturbation theory. A purposely tailored discrete variable representation anharmonic approach is used to treat the LAMs related to internal rotations. The computed spectroscopic data, particularly those in the infrared region, complement the available experimental investigations, thus enhancing the possibility of an astronomical detection of this molecule

The radiative efficiency and global warming potential of HCFC-132b

Hydro-chloro-fluoro-carbons (HCFCs) are potent greenhouse gases which strongly absorb the infrared (IR) radiation within the 8 – 12 μm atmospheric windows. Despite international policies schedule their phasing out by 2020 for developed countries and 2030 globally, HCFC-132b (CH2ClCClF2) has been recently detected with significant atmospheric concentration. In this scenario, detailed climate metrics are of paramount importance for understanding the capacity of anthropogenic pollutants to contribute to global warming. In this work, the radiative efficiency (RE) of HCFC-132b is experimentally measured for the first time and used to determine its global warming potential (GWP) over 20-, 100- and 500-year time horizon. Vibrational- and rotational-spectroscopic properties of this molecule are first characterized by exploiting a synergism between Fourier-transform IR (FTIR) spectroscopy experiments and quantum chemical calculations. Equilibrium geometry, rotational parameters and vibrational properties predicted theoretically beyond the double-harmonic approximation, are employed to assist the vibrational assignment of the experimental trace. Finally, FTIR spectra measured over a range of pressures are used to determine HCFC-132b absorption cross section spectrum from 150 to 3000 cm−1, from which istantaneous and effective REs are derived and, in turn, used for GWP evaluation

Accurate Structure and Spectroscopic Properties of Azulene and Its Derivatives by Means of Pisa Composite Schemes and Vibrational Perturbation Theory to Second Order

The structural and spectroscopic properties in the gas phase of azulene and some of its N-bearing derivatives have been analyzed by a general computational strategy based on the recent Pisa composite schemes (PCSs). First of all, an accurate semiexperimental equilibrium structure has been derived for azulene and employed to validate the geometrical parameters delivered by different quantum chemical methods. Next, different isomerization energies (azulene to naphthalene, 1-aza-azulene to quinoline and to other isomers) have been computed by an explicitly correlated PCS version employing frozen natural orbitals. Accurate geometries have been obtained by a cheaper PCS variant based on a double-hybrid functional improved by one-parameter bond corrections, with the same functional providing also remarkable harmonic frequencies. The corresponding equilibrium rotational constants show average deviations within 0.1% from experimental results when taking into account anharmonic vibrational corrections obtained by a global hybrid functional. Therefore, reliable computational estimates have been produced for the rotational constants of several nitrogen derivatives (isomeric aza-azulenes and guaiazulene), whose non-negligible dipole moments could allow experimental microwave characterizations. An analogous approach delivers infrared spectra in remarkable agreement with their experimental counterparts for naphthalene, quinoline, and azulene, together with reliable predictions for the still-unknown spectrum of 1-aza-azulene. In addition to their intrinsic interest, the results of this paper further confirm that a very accurate yet robust and user-friendly tool is now available for aiding high-resolution spectroscopic studies of quite large systems of current technological and/or biological interest

Theory Meets Experiment for Noncovalent Complexes: The Puzzling Case of Pnicogen Interactions

A gas-phase nitrogen\u2013nitrogen noncovalent interaction has been unveiled in the nitroethane\u2013trimethylamine complex in an environment free from solvent and matrix effects using rotational spectroscopy in supersonic expansion. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C 12H c5 c5 c5O and C 12H c5 c5 c5N hydrogen bonds. Furthermore, a SAPT analysis shows that electrostatic and dispersion interactions play a comparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination

Understanding the complex organisational processes that help and hinder creativity and innovation

This study looks at the topics of creativity and innovation and how they are experienced as ordinary, everyday work. In business publications there is much hype and hope around the words “creativity” and “innovation”, but there is also a limited understanding of how creativity and innovation are enacted in organisations. Consequently, academics have stressed the need for ‘opening the black box’ of the firm and understanding how innovation really works (Birdi et al, 2003). This research uses the Complex Responsive Processes approach to understand the ordinary, everyday experiences of people involved in work which was novel for the organisations concerned. I selected three organisational cases from the health and education sectors. I selected these because, in each case, people were working on complex challenges which had no single, obvious solution and which required the generation and development of new and useful ideas. The research makes a novel contribution to knowledge in three ways. First, it has been unusual in that it has extended the application of complex responsive processes to understand the processes which impact on creativity and innovation in the health and education sectors. While complex responsive processes thinking has been applied to these sectors before, to my knowledge, this is the first time it has been applied to understand processes impacting on creativity and innovation in these sectors. Second, this research finds a pattern of dynamics between trust and a paradoxical concept of diversity, comprising both sufficient difference and sufficient common-ground between organizational members. In this research, trust was a necessary foundation for the exploration of ideas. However, for risks to be taken and ideas to be implemented, in contexts of high uncertainty and risk, trust alone was insufficient. The quality of conversational life flourished where both trust and diversity were present. Finally, this research makes a methodological contribution through using Stacey’s five areas for focusing attention as a conceptual framework. The use of this framework helps provide a depth of compelling detail and insights which would not have been obtained through traditional lenses from the domains of creativity and innovation. This is the first time this framework for focusing attention has been applied in this way to understanding creativity and innovation in empirical settings.EThOS - Electronic Theses Online ServiceGBUnited Kingdo