A LABORATORY AND THEORETICAL STUDY OF PROTONATED CARBON DISULFIDE, HSCS+^+

Author Institution: Harvard-Smithsonian Center for Astrophysics, 60 Garden St.; Cambridge, MA 02138, and School of Engineering \& Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138; Center for Computational Chemistry, University of Georgia, 1004 Cedar St, Athens, GA 30602The rotational spectrum of protonated carbon disulfide, HSCS$^+$, has been detected in the centimeter-wave band in a molecular beam by Fourier transform microwave spectroscopy. Rotational and centrifugal distortion constants have been determined from transitions in the $K_a=0$ ladder of the normal isotopic species, HS$^{13}$CS$^+$, and DSCS$^+$. The present assignment agrees well with high-level coupled cluster calculations of the HSCS$^+$ structure, which, like earlier work, predict this isomer to be the ground state on the HCS$_2^+$ potential energy surface; HCSS$^+$, an isomer with $C_{2v}$ symmetry, is predicted to lie more than 20~kcal/mol higher in energy. Other properties of HSCS$^+$ including its dipole moment, vibrational frequencies, and infrared intensities have also been calculated at the CCSD(T)/cc-pwCVQZ level of theory. Because carbon disulfide possesses a fairly large proton affinity, and because this nonpolar molecule may plausible exist in astronomical sources, HSCS$^+$ is a good candidate for detection with radio telescopes in the sub-millimeter band where the stronger $b$-type transitions of this protonated cation are predicted to lie

APHiD: Hierarchical Task Placement to Enable a Tapered Fat Tree Topology for Lower Power and Cost in HPC Networks:

The power and procurement cost of bandwidth in system-wide networks has forced a steady drop in the byte/flop ratio. This trend of computation becoming faster relative to the network is expected to hold. In this paper, we explore how cost-oriented task placement enables reducing the cost of system-wide networks by enabling high performance even on tapered topologies where more bandwidth is provisioned at lower levels. We describe APHiD, an efficient hierarchical placement algorithm that uses new techniques to improve the quality of heuristic solutions and reduces the demand on high-level, expensive bandwidth in hierarchical topologies. We apply APHiD to a tapered fat-tree, demonstrating that APHiD maintains application scalability even for severely tapered network configurations. Using simulation, we show that for tapered networks APHiD improves performance by more than 50% over random placement and even 15% in some cases over costlier, state-of-the-art placement algorithms

APHiD: Hierarchical Task Placement to Enable a Tapered Fat Tree Topology for Lower Power and Cost in HPC Networks:

The power and procurement cost of bandwidth in system-wide networks has forced a steady drop in the byte/flop ratio. This trend of computation becoming faster relative to the network is expected to hold. In this paper, we explore how cost-oriented task placement enables reducing the cost of system-wide networks by enabling high performance even on tapered topologies where more bandwidth is provisioned at lower levels. We describe APHiD, an efficient hierarchical placement algorithm that uses new techniques to improve the quality of heuristic solutions and reduces the demand on high-level, expensive bandwidth in hierarchical topologies. We apply APHiD to a tapered fat-tree, demonstrating that APHiD maintains application scalability even for severely tapered network configurations. Using simulation, we show that for tapered networks APHiD improves performance by more than 50% over random placement and even 15% in some cases over costlier, state-of-the-art placement algorithms

Topology-Aware Performance Optimization and Modeling of Adaptive Mesh Refinement Codes for Exascale

We introduce a topology-aware performance optimization and modeling workflow for AMR simulation that includes two new modeling tools, ProgrAMR and Mota Mapper, which interface with the BoxLib AMR framework and the SSTmacro network simulator. ProgrAMR allows us to generate and model the execution of task dependency graphs from high-level specifications of AMR-based applications, which we demonstrate by analyzing two example AMR-based multigrid solvers with varying degrees of asynchrony. Mota Mapper generates multiobjective, network topology-aware box mappings, which we apply to optimize the data layout for the example multigrid solvers. While the sensitivity of these solvers to layout and execution strategy appears to be modest for balanced scenarios, the impact of better mapping algorithms can be significant when performance is highly constrained by network hop latency. Furthermore, we show that network latency in the multigrid bottom solve is the main contributing factor preventing good scaling on exascale-class machines

1-Germavinylidene (GeCH₂), Germyne (HGeCH), and 2-Germavinylidene (H₂GeC) Molecules and Isomerization Reactions among Them: Anharmonic Rovibrational Analyses

Theoretical investigations of three equilibrium structures and two associated isomerization reactions of the GeCH₂ - HGeCH - H₂GeC system have been systematically carried out. This research employed ab initio self-consistent-field (SCF), coupled cluster (CC) with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD­(T)] wave functions and a wide variety of correlation-consistent polarized valence cc-pV<i>X</i>Z and cc-pV<i>X</i>Z-DK (where <i>X</i> = D, T, Q) basis sets. For each structure, the total energy, geometry, dipole moment, harmonic vibrational frequencies, and infrared intensities are predicted. Complete active space SCF (CASSCF) wave functions are used to analyze the effects of correlation on physical properties and energetics. For each of the equilibrium structures, vibrational second-order perturbation theory (VPT2) has been utilized to obtain the zero-point vibration corrected rotational constants, centrifugal distortion constants, and fundamental vibrational frequencies. The predicted rotational constants and anharmonic vibrational frequencies for 1-germavinylidene are in good agreement with available experimental observations. Extensive focal point analyses, including CCSDT and CCSDT­(Q) energies and basis sets up to quintuple zeta, are used to obtain complete basis set (CBS) limit energies. At all levels of theory employed in this study, the global minimum of the GeCH₂ potential energy surface (PES) is confirmed to be 1-germavinylidene (GeCH₂, <b>1</b>). The second isomer, germyne (HGeCH, <b>2</b>) is predicted to lie 40.4(41.1) ± 0.3 kcal mol^–1 above the global minimum, while the third isomer, 2-germavinylidene (H₂GeC, <b>3</b>) is located 92.3(92.7) ± 0.3 kcal mol^–1 above the global minimum; the values in parentheses indicate core–valence and zero-point vibration energy (ZPVE) corrected energy differences. The barriers for the forward (<b>1</b>→<b>2</b>) and reverse (<b>2</b>→<b>1</b>) isomerization reactions between isomers <b>1</b> and <b>2</b> are 48.3(47.7) ± 0.3 kcal mol^–1 and 7.9(6.6) ± 0.3 kcal mol^–1, respectively. On the other hand, the barriers of the forward (<b>2</b>→<b>3</b>) and reverse (<b>3</b>→<b>2</b>) isomerization reactions between isomers <b>2</b> and <b>3</b> are predicted to be 55.2(53.2) ± 0.3 kcal mol^–1 and 3.3(1.6) ± 0.3 kcal mol^–1, respectively