212 research outputs found
Exploding Nitromethane in silico, in real time
Nitromethane (NM) is widely applied in chemical technology as a solvent for
extraction, cleaning and chemical synthesis. NM was considered safe for a long
time, until a railroad tanker car exploded in 1958. We investigate detonation
kinetics and reaction mechanisms in a variety of systems consisting of NM,
molecular oxygen and water vapor. State-of-the-art reactive molecular dynamics
allows us to simulate reactions in time-domain, as they occur in real life.
High polarity of the NM molecule is shown to play an important role, driving
the first exothermic step of the reaction. Presence of oxygen is important for
faster oxidation, whereas its optimal concentration is in agreement with the
proposed reaction mechanism. Addition of water (50 mol%) inhibits detonation;
however, water does not prevent detonation entirely. The reported results
provide important insights for improving applications of NM and preserving
safety of industrial processes.Comment: arXiv admin note: text overlap with arXiv:1408.372
Polarization versus Temperature in Pyridinium Ionic Liquids
Electronic polarization and charge transfer effects play a crucial role in
thermodynamic, structural and transport properties of room-temperature ionic
liquids (RTILs). These non-additive interactions constitute a useful tool for
tuning physical chemical behavior of RTILs. Polarization and charge transfer
generally decay as temperature increases, although their presence should be
expected over an entire condensed state temperature range. For the first time,
we use three popular pyridinium-based RTILs to investigate temperature
dependence of electronic polarization in RTILs. Atom-centered density matrix
propagation molecular dynamics, supplemented by a weak coupling to an external
bath, is used to simulate the temperature impact on system properties. We show
that, quite surprisingly, non-additivity in the cation-anion interactions
changes negligibly between 300 and 900 K, while the average dipole moment
increases due to thermal fluctuations of geometries. Our results contribute to
the fundamental understanding of electronic effects in the condensed phase of
ionic systems and foster progress in physical chemistry and engineering
A New Model of Chemical Bonding in Ionic Melts
We developed a new physical model to predict macroscopic properties of
inorganic molten systems using a realistic description of inter-atomic
interactions. Unlike the conventional approach, which tends to overestimate
viscosity by several times, our systems consist of a set of ions with an
admixture of neutral atoms. The neutral atom subsystem is a consequence of the
covalent/ionic state reduction, occurring in the liquid phase. Comparison of
the calculated macroscopic properties (shear viscosity and self-diffusion
constants) with the experiment demonstrates good performance of our model. The
presented approach is inspired by a significant degree of covalent interaction
between the alkali and chlorine atoms, predicted by the coupled cluster theory
Excited States of Positronic Lithium and Beryllium
Using a variational method with an explicitly correlated Gaussian basis, we study the eþ-Li and eþ-Be
complexes in the ground and lowest excited states with higher spin multiplicity. Our calculations provide
rigorous theoretical confirmation that a positron can be attached to the excited states: 1s2s2p 4Po and
1s22s2p 3Po for eþ-Li and eþ-Be, respectively. The result is particularly notable for the eþ-Be complex,
as the excited 3Po state lies below the autoionization threshold. We report accurate binding energies,
annihilation rates and structural properties of these positron-atom systems. The existence of the ground
and metastable excited states with bound positron opens up a new route to the presently lacking
experimental verification of stability of a positron binding to any neutral ato
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