Kinetics and dynamics for chemical reactions in gas phase

A deep understanding of molecular reactions is a challenging task since the range of time and energy covered implies a wide and dense grid for the numerical representation of the reactive Hamiltonian. For a computational chemist, the accurate prediction of its value starting from the definition of reactants and products is fascinating and demanding, but can be extremely useful for further investigation and optimization problems. Several methods, all derived by the Transition State Theory, have been developed to avoid the computational cost of the Hamiltonian representation on a large, multidimensional grid; we investigate these strategies both in the time and energy domain to explore the advan- tages and drawbacks of these reciprocal spaces. Since we want to increase the range of applicability of the calcula- tion of thermal rate constants to medium size molecules, which can have floppy geometries with low frequency modes, we introduce a dedicated treatment of such modes based on the Intrinsic Reaction Path of Fukui. In Part i, we introduce the theoretical instrument used to perform our calculation, both in energy and time domain; Part ii is devoted to the presentation of the applications, mainly focused on current issues in astrochemical studies. Appendices treat specific topics, like M\uf6ller operators, essential for the comprehension of the theory but too long to be inserted in Part i

Ab initio instanton rate theory made efficient using Gaussian process regression

Ab initio instanton rate theory is a computational method for rigorously including tunnelling effects into calculations of chemical reaction rates based on a potential-energy surface computed on the fly from electronic-structure theory. This approach is necessary to extend conventional transition-state theory into the deep-tunnelling regime, but is also more computationally expensive as it requires many more ab initio calculations. We propose an approach which uses Gaussian process regression to fit the potential-energy surface locally around the dominant tunnelling pathway. The method can be converged to give the same result as from an on-the-fly ab initio instanton calculation but requires far fewer electronic-structure calculations. This makes it a practical approach for obtaining accurate rate constants based on high-level electronic-structure methods. We show fast convergence to reproduce benchmark H + CH4 results and evaluate new low-temperature rates of H + C2H6 in full dimensionality at a UCCSD(T)-F12b/cc-pVTZ-F12 level.Comment: 12 pages, 4 figures; submitted to Faraday Discussion: Quantum effects in small molecular system

LHF Connect: a DIY telepresence robot against COVID-19

This contribution describes a case study of a “do-it-yourself” (DIY) opensource service and related product to help combating the COVID-19 emergency. It illustrates the birth of LHF Connect, a project designed to facilitate communication between patients isolated in COVID-19 hospitals’ ward and their relatives. LHF Connect is a teleoperated robot that can move in autonomy around the hospital. A User Centered Design approach, methods and specific tools helped in managing crucial steps of the design process such as i) the collection of needs coming from the context, stakeholders and end-users; ii) defining the service blueprint; iii) imagining finishing concepts; and iv) managing the communication activities. The initiative has been promoted by a multidisciplinary team of researchers (mainly roboticists with the help of specific competences coming from Design discipline)

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements