Atanu Bhattacharya

Location aware resource management in smart homes

The rapid advances in a wide range of wireless access technologies along with the efficient use of smart spaces have already set the stage for the development of smart homes. Context-awareness is perhaps the most salient feature in these intelligent computing platforms. The location information of the users plays a vital role in defining this context. To extract the best performance and efficacy of such smart computing environments, one needs a scalable, technology-independent location service. We have developed a predictive framework for location-aware resource optimization in smart homes. The underlying compression mechanism helps in efficient learning of an inhabitants movement (location) profiles in the symbolic domain. The concept of Asymptotic Equipartition Property (AEP) in information theory helps to predict the inhabitants future location as well as most likely path-segments with good accuracy. Successful prediction helps in pro-active resource management and on-demand operations of automated devices along the inhabitants future paths and locations - thus providing the necessary comfort at a near-optimal cost. Simulation results on a typical smart home floor plans corroborate this high prediction success and demonstrate sufficient reduction in daily energy-consumption, manual operations and time spent by the inhabitant which are considered as a fair measure of his/her comfort.

On the ultrafast charge migration and subsequent charge directed reactivity in Cl⋯N halogen-bonded clusters following vertical ionization

In this article, we have presented ultrafast charge transfer dynamics through halogen bonds following vertical ionization of representative halogen bonded clusters. Subsequent hole directed reactivity of the radical cations of halogen bonded clusters is also discussed. Furthermore, we have examined effect of the halogen bond strength on the electron-electron correlation- and relaxation-driven charge migration in halogen bonded complexes. For this study, we have selected A-Cl (A represents F, OH, CN, NH2, CF3, and COOH substituents) molecules paired with NH3 (referred as ACl:NH3 complex): these complexes exhibit halogen bonds. To the best of our knowledge, this is the first report on purely electron correlation- and relaxation-driven ultrafast (attosecond) charge migration dynamics through halogen bonds. Both density functional theory and complete active space self-consistent field theory with 6-31 + G(d, p) basis set are employed for this work. Upon vertical ionization of NCCl⋯NH3 complex, the hole is predicted to migrate from the NH3-end to the ClCN-end of the NCCl⋯NH3 complex in approximately 0.5 fs on the D0 cationic surface. This hole migration leads to structural rearrangement of the halogen bonded complex, yielding hydrogen bonding interaction stronger than the halogen bonding interaction on the same cationic surface. Other halogen bonded complexes, such as H2NCl:NH3, F3CCl:NH3, and HOOCCl:NH3, exhibit similar charge migration following vertical ionization. On the contrary, FCl:NH3 and HOCl:NH3 complexes do not exhibit any charge migration following vertical ionization to the D0 cation state, pointing to interesting halogen bond strength-dependent charge migration.

Excited electronic state decomposition mechanisms of clusters of dimethylnitramine and aluminum

AbstractIn this report, electronically non-adiabatic decomposition pathways of clusters of dimethylnitramine and aluminum (DMNA-Al and DMNA-Al2) are discussed in comparison to isolated dimethylnitramine (DMNA). Electronically excited state processes of DMNA-Al and DMNA-Al2 are explored using the complete active space self-consistent field (CASSCF) and the restricted active space self-consistent field (RASSCF) theories, respectively. Similar to the nitro-nitrite isomerization reaction pathway of DMNA, DMNA-Aln clusters also exhibit isomerization pathway. However, it involves several other steps, such as, first Al-O bond dissociation, then N-N bond dissociation followed by isomerization and finally NO elimination. Furthermore, DMNA-Aln clusters exhibit overall exothermic decomposition reaction pathway and isolated DMNA shows overall endothermic reaction channel.n Graphical AbstractIn the electronically non-adiabatic decomposition mechanism of DMNA-Al cluster, it is predicted that NO elimination is followed by the nitro-nitrite isomerization as the primary decomposition channel.

On the Attosecond charge migration in Cl…..N, Cl…..O, Br…..N and Br…..O Halogen-bonded clusters: Effect of donor, acceptor, vibration, rotation, and electron correlation

AbstractThe electron-electron relaxation and correlation-driven charge migration process, which features pure electronic aspect of ultrafast charge migration phenomenon, occurs on a very short timescale in ionized molecules and molecular clusters, prior to the onset of nuclear motion. In this article, we have presented nature of ultrafast pure electronic charge migration dynamics through Cl…..N, Cl…..O, Br…..N, and Br…..O halogen bonds, explored using density functional theory. We have explored the role of donor, acceptor, electron correlation, vibration and rotation in charge migration dynamics through these halogen bonds. For this work, we have selected ClF, Cl2, ClOH, ClCN, BrF, BrCl, BrOH, and BrCN molecules paired with either NH3 or H2O. We have found that the timescale for pure electron-electron relaxation and correlation-driven charge migration through the Cl…..N, Br…..N, Cl…..O, and Br…..O halogen bonds falls in the range of 300–600 attosecond. The primary driving force behind the attosecond charge migration through the Cl…..N, Br…..N, Cl…..O, and Br…..O halogen bonds is the energy difference (ΔE) between two stationary cationic orbitals (LUMO- β and HOMO- β), which together represents the initial hole density immediately following vertical ionization. We have also predicted that the strength of electron correlation has significant effect on the charge migration timescale in Cl…..N, Br…..N, Cl…..O, and Br…..O halogen bonded clusters. Vibration and rotation are also found to exhibit profound effect on attosecond charge migration dynamics through halogen bonds.n Graphical AbstractThe attosecond charge migration dynamics through Cl…..N, Cl…..O, Br…..N, and Br…..O halogen bonds depends on strength of electron correlation, donor and acceptor, the energy difference (ΔE) between two stationary cationic orbitals (LUMO-β and HOMO-β) involved in electronic superposition, vibration and rotation.

Sub-500 fs electronically nonadiabatic chemical dynamics of energetic molecules from the S1 excited state: Ab initio multiple spawning study

Energetic materials store a large amount of chemical energy. Different ignition processes, including laser ignition and shock or compression wave, initiate the energy release process by first promoting energetic molecules to the electronically excited states. This is why a full understanding of initial steps of the chemical dynamics of energetic molecules from the excited electronic states is highly desirable. In general, conical intersection (CI), which is the crossing point of multidimensional electronic potential energy surfaces, is well established as a controlling factor in the initial steps of chemical dynamics of energetic molecules following their electronic excitations. In this article, we have presented different aspects of the ultrafast unimolecular relaxation dynamics of energetic molecules through CIs. For this task, we have employed ab initio multiple spawning (AIMS) simulation using the complete active space self-consistent field (CASSCF) electronic wavefunction and frozen Gaussian-based nuclear wavefunction. The AIMS simulation results collectively reveal that the ultrafast relaxation step of the best energetic molecules (which are known to exhibit very good detonation properties) is completed in less than 500 fs. Many, however, exhibit sub-50 fs dynamics. For example, nitro-containing molecules (including C-NO2, N-NO2, and O-NO2 active moieties) relax back to the ground state in approximately 40 fs through similar (S1/S0)CI conical intersections. The N3-based energetic molecule undergoes the N2 elimination process in 40 fs through the (S1/S0)CI conical intersection. Nitramine-Fe complexes exhibit sub-50 fs Fe-O and N-O bond dissociation through the respective (S1/S0)CI conical intersection. On the other hand, tetrazine-N-oxides, which are known to exhibit better detonation properties than tetrazines, undergo internal conversion in a 400-fs time scale, while the relaxation time of tetrazine is very long (about 100 ns). Many other characteristics of sub-500 fs nonadiabatic decay of energetic molecules are discussed. In the end, many unresolved issues associated with the ultrafast nonadiabatic chemical dynamics of energetic molecules are presented.