Studies of electron collisions with polyatomic molecules using distributed-memory parallel computers

Abstract

Elastic electron scattering cross sections from 5-30 eV are reported for the molecules C H C 2 H 6 , C 3 Hs, Si 2 H 6 , and GeH 4 , obtained using an implementation of the Schwinger 2 4' multichannel method for distributed-memory parallel computer architectures. These results, obtained within the static-exchange approximation, are in generally good agreement with the available experimental data. These calculations demonstrate the potential of highly parallel computation in the study of collisions between low-energy electrons and polyatomic gases. The computational methodology discussed is also directly applicable to the calculation of elastic cross sections at higher levels of approximation (target polarization) and of electronic excitation cross sections.

Elastic Cross Sections for Electron Collisions with Molecules Relevant to Plasma Processing

“…Schwinger multichannel theoretical approach 54,55 reported corresponding cross sections for electron energies in the range 5 -30 eV. Generally quite good agreement was found between the results from these calculations and the data of Dillon et al, 53 so our recommended data in Table 21 below …”

“…Thereafter, the only comprehensive experimental study, which reported elastic DCS, ICS, and MTCS for energies between 1.5 and 100 eV and scattering angles of 10°-130°, was published by Dillon et al 58 Subsequently, a Schwinger multichannel theoretical approach 54 reported corresponding cross sections for electron energies in the range 5 -30 eV. Recently, two other calculations have also been reported.…”

Recent advances in the application of the Schwinger multichannel method with pseudopotentials to electron-molecule collisions

“…In this procedure, the radial k-space is discretized on the quadrature points {k j }, where the g m μν (k j ) matrix elements are calculated, and the {k l } angular quadratures are also employed to obtain the g m μν elements, according to equation (35). While this numerical integration is significantly more demanding than the previous implementation based on a numerically complete single-particle space, it provides a faster convergence with respect to the Gaussian basis sets and proved to be more stable and reliable over a large number of applications.…”

“…Historically, the evolution of the method went through the following steps: (1) Cartesian Gaussian insertion with the computer code running in central memory [30,31]; (2) numerical integration of the residue part of the V G (+) P V term 2 ; (3) NASA's reorganization of the computer codes aiming at intense use of I/O (disk memory instead of central memory) [33,34]. From this point two different versions of the program evolved in different ways, the version at Caltech bet on: (4) parallelization of the computer codes [35]; while the version at the State University of Campinas (UNICAMP) returned to a central memory strategy and bet on: (5) the use of norm-conserving pseudopotentials (SMCPP) [36]; both versions relied on a (6) three-dimension integration of the V G (+) P V term [37]. From this point, the Brazilian version that produced the results described in this paper evolved to: (7) single excitation configuration interaction for the target description of the excited states and a strategy of a minimal orbital basis for single configuration interaction (MOBSCI) [38] for choosing the appropriate and feasible level of multichannel coupling computation; and finally moved to (8) consolidation of the central memory strategy with parallelization of the computer codes with all properties cited above [39].…”

Developing Cross Section Sets for Fluorocarbon Etchants

“…We have developed a computational method, the Schwinger Multichannel or SMC method [2,3], that is specifically intended to treat inelastic as well as elastic collisions of low-energy electrons with polyatomic molecules, and we have adapted the SMC method to run efficiently on parallel computers [4,5,6,7], which provide the resources necessary to carry out large-scale computations. We have applied the parallel SMC method to obtain elastic and inelastic electron cross sections for a variety of molecules, with generally good results [8,9,10,11].…”