Molecular Physics of Elementary Processes relevant to Hypersonics: atom-molecule, molecule-molecule and atom-surface processes.

In the present chapter some prototype gas and gas-surface processes occurring within the hypersonic flow layer surrounding spacecrafts at planetary entry are discussed. The discussion is based on microscopic dynamical calculations of the detailed cross sections and rate coefficients performed using classical mechanics treatments for atoms, molecules and surfaces. Such treatment allows the evaluation of the efficiency of thermal processes (both at equilibrium and nonequilibrium distributions) based on state-to-state and state specific calculations properly averaged over the population of the initial states. The dependence of the efficiency of the considered processes on the initial partitioning of energy among the various degrees of freedom is discussed

Full Dimensional Potential Energy Function and Calculation of State-Specific Properties of the CO+N2 Inelastic Processes Within an Open Molecular Science Cloud Perspective

A full dimensional Potential Energy Surface (PES) of the CO + N2 system has been generated by extending an approach already reported in the literature and applied to N2-N2 (Cappelletti et al., 2008), CO2-CO2 (Bartolomei et al., 2012), and CO2-N2 (Lombardi et al., 2016b) systems. The generation procedure leverages at the same time experimental measurements and high-level ab initio electronic structure calculations. The procedure adopts an analytic formulation of the PES accounting for the dependence of the electrostatic and non-electrostatic components of the intermolecular interaction on the deformation of the monomers. In particular, the CO and N2 molecular multipole moments and electronic polarizabilities, the basic physical properties controlling the behavior at intermediate and long-range distances of the interaction components, were made to depend on relevant internal coordinates. The formulated PES exhibits substantial advantages when used for structural and dynamical calculations. This makes it also well suited for reuse in Open Molecular Science Cloud services

Molecular simulations as test beds for bridging high throughput and high performance computing

La forte connotation de la chimie computationnelle en termes de technologies informatiques est en même temps la force et la faiblesse des simulations moléculaires. En effet, dans le but de réaliser des études de ce type(même pour les systèmes contenant un petit nombre d'atomes), il faut d'abord procéder à des calculs de structure électronique de haut niveau. Ces calculs nécessitent généralement des nœuds (ou clusters de nœuds) équipés de mémoires de grande taille (de l'ordre de plusieurs Go), et de processeurs performants au niveau de plusieurs Gigaflops. Celà parce que la surface d'énergie potentielle ensemble (PES) qui régît le mouvement nucléaire doit être élaborée préalablement. Sur des plate-formes High Performance Computing (HPC) avec des capacités parallèles améliorées nous pouvons exécuter simultanément, sur plusieurs single (ou clusters de) processeurs multicœurs, le calculs requis par le grand nombre des valeurs d'énergie potentielles nécessaires pour décrire les PES explorés par une processus de réactivité chimique. Le véritable goulot d'étranglement dans la réalisation des calculs nécessaires, en effet, est représentée par la disponibilité d'une plate-forme informatique ayant des exigences informatiques appropriées en matière de temps de calcul et de mémoire physique. Les capacités de calcul (limitée) en général accessibles à la communauté scientifique, en fait, a toujours fixé des limites sévères à l'élaboration d'un système informatique complet de simulation a priori des processus moléculaires. Heureusement, des technologies informatiques innovantes, alliant la concurrence et la mise en réseau (tels que l'informatique distribuée, les laboratoires virtuels, le calcul intensif, le "Grid computing") ouvrent des perspectives nouvelles à la possibilité de réaliser d'importants débits de calcul et, par conséquent, de développer des simulations moléculaires a priori des systèmes réels. Les fondements théoriques et les paradigmes informatiques utilisés pour l'assemblage des composants du "Grid Empowered Molecular Simulator" (GEMS) sont décrits dans le Chapitre 1. Dans ce chapitre, nous illustrons le développement de workflows basés sur la grille, qui permettent l'évaluation ab initio des propriétés observables des systèmes chimiques petits à partir du calcul des propriétés électroniques. Dans le chapitre 2 nous abordons la question de l'interopérabilité entre codes de calcul à travers les différentes étapes du flux de travail (workflow). Ce chapitre propose les formats Q5cost et D5cost comme modèles "standard de facto" pour les calculs de chimie quantique. Le Chapitre 3 porte sur les résultats de calculs ab initio autonomes effectués sur des différents systèmes chimiques (petits clusters X_4 (X=Li,Na,K,Cu) ainsi que le dimère BeH-). Le chapitre traite des liaisons chimiques particulières et intéressantes présentes dans ces systèmes, qui nécessitent de méthodes quantiques de haut niveau à fin d'une possible rationalisation. Enfin, les chapitre 4 et 5 concernent respectivement les résultats de notre travail sur deux problèmes de combustion et la chimie atmosphérique (l'isomérisation CH3CH2OO• et la réaction N2+N2). Ils visent tous les deux à la construction des PES pour un processus réactif. Une fois la PES générée, les données cinétiques et dynamiques doivent être calculées pour un grand nombre de conditions initiales, et cela peut être fait sur des plateformes HTC. L'assemblage des workflows informatiques pour l'utilisation couplée des systèmes HPC et HTC est également traitée dans cette thèse.The strong connotation of computational chemistry in terms of computer technologies is at the same time the strength and the weakness of molecular simulations. As a matter of fact, in order to perform such studies (even for few-atom systems) we first need to carry out high-level electronic structure calculations. These calculations typically require nodes (or clusters of nodes) equipped with large (of the order of many GB) memories and processors performing at the level of several Gigaflops. This is because the whole Potential Energy Surface (PES) governing the nuclear motion needs to be worked out first. On the High Performance Computing (HPC) platforms with enhanced parallel capabilities we can run concurrently, on several single multicore (or clusters of) processors, the calculations required by the (large number of) potential energy values necessary to describe the PES explored by a reactive chemical process. The real bottleneck in carrying out related computational campaigns, indeed, is represented by the availability of a computing platform having the proper computational requirements in terms of computing time and physical memory. The (limited) computing capabilities in general available to the scientific community, in fact, still set severe limitations to the development of full a priori computational simulations of molecular processes. Fortunately, innovative computing technologies combining concurrency and networking (such as distributed computing, virtual laboratories, supercomputing, Grid computing) are opening new prospects to the possibility of achieving significant computational throughputs and, therefore, of developing a priori molecular simulations of real systems. The theoretical foundations and the computing paradigms employed for the assemblage of the components of the Grid Empowered Molecular Simulator GEMS are described in Chapter 1. In that chapter the development of grid based workflows allowing the ab initio evaluation of the observable properties of small chemical systems starting from the calculation of the electronic properties is illustrated. In Chapter 2 the issue of the of interoperability between computational codes across different stages of the workflow is faced. The Chapter proposes Q5cost and D5cost common data models as de facto standard formats for quantum chemistry calculations. Chapter 3 relates to the results of standalone ab initio calculations performed on different small chemical systems (X4 clusters and BeH- dimer). The Chapter discusses particular and interesting chemical bonds requiring high-level quantum methods to the end of being rationalized. Finally Chapter 4 and Chapter 5 report the results of our work on two combustion and atmospheric chemistry problems (CH3CH2OO• isomerization and N2+N2 reaction) respectively. They both aim at constructing the PES for a reactive process. Once a PES is generated, the kinetic and dynamical data need to be calculated for a large number of initial conditions, and can be computed on HTC platforms. The assemblage of the computational workflows for the coupled use of HPC and HTC systems is also dealt there

Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong non-equilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electron-impact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N2, O2, NO), Mars (CO2, CO, N2) and Jupiter (H2, He) atmospheres are considered

Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong non-equilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electron-impact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N-2, O-2, NO), Mars (CO2, CO, N-2) and Jupiter (H-2, He) atmospheres are considered

A study of the impact of long range interactions on the reactivity of N + N2 using the Grid Empowered Molecular Simulator GEMS

The Potential Energy Surface (PES) of the N + N2 atom diatom system has been reformulated using the Largest Angle Generalisation of the Rotating Bond Order (LAGROBO) functional form for interpolating ab initio points in the short distance region and using a modified Lennard-Jones functional form to model the van der Waals interaction at long range. On the proposed surface extended quantum calculations have been performed using the Dynamics module of the Grid Empowered Molecular Simulator (GEMS) on the European Grid platform. The values of the calculated thermal rate coefficients fairly well reproduce the experimental results. Copyright \uc2\ua9 2010 Inderscience Enterprises Ltd

Research and technology operating plan: A summary Fiscal Year 1974

A compilation is presented of the summary portions of RTOPs used for management review and control of research. Citations and abstracts of RTOPs are included. A list is presented of RTOPs which have been changed, completed, or terminated since the last summary. Indexes presented include: subject, technical monitor, responsible NASA organization, and RTOP number

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen