Robert A. Whiteside

Structures of small carbon clusters: Cyclic ground state of C6

Accurate ab initio calculations have been performed to investigate the nature of the structures and energies of different C6 isomers. The effects of polarization functions and electron correlation have been included in these calculations. A cyclic singlet structure with six π electrons (planar D3h,1A’) is found to be the ground state. The linear 3Σ−g structure lies about 10 kcal/mol higher in energy. The heat of formation, ΔH°0, of C6 is estimated to be ∼281 kcal/mol.

Structures of C4

Abstract Linear ( 1 ), cyclic ( 2 ) and bicyclic ( 3 ) alternatives are considered as possible ground-state structures for C 4 . At the highest levels of theory, MP4SDQ/6-31 ∗ //HF/6-31 ∗ , 3, with two π electrons is found to be most stable.

Cyclic C3 structures

Abstract Alternative cyclic C3 structures are not competitive energetically with the linear 1∑g+ ground state, 1. The D3h triplet, 4, is a local minimum on the potential energy surface. Cyclopropynylidene, a C2v singlet (3) is a saddle point for the degenerate isomerization which permutes the order of carbon atoms in 1. The activation energy for this transformation is predicted to be 29 kcal mole .

The structure of CCH

Molecular orbital theory is used to examine relative energies of low‐lying electronic states of the ethynyl cation CCH+. A triplet 3ru is found to be the ground state at the highest level of theory with another triplet 3J− only 2.4 kcal/mole higher in energy. The closed‐shell 1J+ state lies 59 kcal/mole above the ground state.

A Case Study in the Application of a Tightly Coupled Multiprocessor to Scientific Computations

Publisher Summary Computational physicists, chemists, and biologists need hardware and software facilities that are capable of solving numerical problems. Processors that are capable of executing several operations are a cost-effective way of supplying these needs than are serial computers. This chapter presents the experiments designed to understand the potential of a general-purpose tightly coupled multiprocessor. It describes the hardware and software characteristics of multiprocessors. From the hardware engineering point of view, multiprocessors may offer attractive solutions to the problem of increasing the performance of computers than the parallel machines, because they are able to take advantage of simple regular designs, which employ replicated standard components. When suitable communication structures are used, they allow extensibility and reliability. To a certain extent, the regularity of the design is achieved at the expense of removing specialized and centralized control, and one of the characteristics of software that executes on multiple instruction, multiple data (MIMD) machines is the need to provide control using a variety of programming techniques. This involves software overheads, in terms of design complexity and execution costs.