Electron Scattering by Small Molecules

Winstead, Carl; McKoy, Vincent

doi:10.1002/9780470141557.ch3

Cited by 17 publications

(10 citation statements)

References 232 publications

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“…In terms of a scattering theory based approach, [55] the resonance parameters can be extracted from the scattering cross-section or phase shift. Complex Kohn method, [88,89] Schwinger multichannel method, [90,91] Schwinger variational method, [89,92] R-matrix method [93][94][95][96][97] are the notable examples of this approach. The scattering theory based methods can handle the continuum nature of the wavefunction efficiently [89,93,94,[98][99][100] but run into trouble when many-body effects are strong.…”

Section: Chemphyschemmentioning

confidence: 99%

“…Complex Kohn method, [88,89] Schwinger multichannel method, [90,91] Schwinger variational method, [89,92] R-matrix method [93][94][95][96][97] are the notable examples of this approach. The scattering theory based methods can handle the continuum nature of the wavefunction efficiently [89,93,94,[98][99][100] but run into trouble when many-body effects are strong. [101] These methods do not afford any chemical insight [102,103] and do not make use of the chemical intuition about the orbitals, charge distributions and their implications for the structural and spectroscopic properties.…”

Section: Chemphyschemmentioning

confidence: 99%

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Recent Advances in the Study of Negative‐Ion Resonances Using Multiconfigurational Propagator and a Complex Absorbing Potential

Das

Samanta

2022

ChemPhysChem

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The transient resonances are a challenge to bound state quantum mechanics. These states lie in the continuum part of the spectrum of the Hamiltonian. For this, one has to treat a continuum problem due to electron‐molecule scattering and the many‐electron correlation problem simultaneously. Moreover, the description of a resonance requires a wavefunction that bridges the part that resembles a bound state with another that resembles a continuum state such that the continuity of the wavefunction and its first derivative with respect to the distance between the incoming projectile and the target is maintained. A review of the recent advances in the theoretical investigation of the negative‐ion resonances (NIR) is presented. The NIRs are ubiquitous in nature. They result from the scattering of electrons off of an atomic or molecular target. They are important for numerous chemical processes in upper atmosphere, space and even biological systems. A contextual background of the existing theoretical methods as well as the newly‐developed multiconfigurational propagator tools based on a complex absorbing potential are discussed.

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Section: Chemphyschemmentioning

confidence: 99%

Section: Chemphyschemmentioning

confidence: 99%

Recent Advances in the Study of Negative‐Ion Resonances Using Multiconfigurational Propagator and a Complex Absorbing Potential

Das

Samanta

2022

ChemPhysChem

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“…Since resonances are embedded and coupled to the continuum, application of standard bound methods to resonances is not straightforward. , Several methods have been developed over the years for the accurate treatment of anion resonances, and with the advent of powerful computers and sophisticated computational algorithms, computing anion resonances of polyatomic systems with increased accuracy has gained more traction. − Explicit treatment of the continuum is possible in scattering theory, and hence, methods based on scattering theory ,,− have established themselves as powerful tools for studying anion resonances and dissociative electron attachment phenomena. On the other hand, numerous modifications to standard Hermitian electronic structure theory have also enabled a plethora of studies on resonances. ,,,, Electronic structure theory based methods have the advantage of being more user-friendly for a quantum chemist compared to scattering methods, and they also enable chemical interpretation of the states in terms of Dyson orbitals, Franck–Condon factors, and so on .…”

Section: Introductionmentioning

confidence: 99%

Projected Complex Absorbing Potential Multireference Configuration Interaction Approach for Shape and Feshbach Resonances

Thodika

Matsika

2022

J. Chem. Theory Comput.

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Anion resonances are formed as metastable intermediates in low-energy electron-induced reactions. Due to the finite lifetimes of resonances, applying standard Hermitian formalism for their characterization presents a vexing problem for computational chemists. Numerous modifications to conventional quantum chemical methods have enabled satisfactory characterization of resonances, but specific issues remain, especially in describing two-particle one-hole (2p–1h) resonances. An accurate description of these resonances and their coupling with single-particle resonances requires a multireference approach. We propose a projected complex absorbing potential (CAP) implementation within the multireference configuration interaction (MRCI) framework to characterize single-particle and 2p–1h resonances. As a first application, we use the projected-CAP-MRCI approach to characterize and benchmark the 2Πg shape resonance in N2 –. We test its performance as a function of the size of the subspace and other parameters, and we compute the complex potential energy surface of the 2Πg shape resonance to show that a smooth curve is obtained. One key benefit of MRCI is that it can describe Feshbach resonances (most common examples of 2p–1h resonances) at the same footing as shape resonances. Therefore, it is uniquely positioned to describe mixing between the different channels. To test these additional capabilities, we compute Feshbach resonances in H2O– and anions of dicyanoethylene isomers. We find that CAP-MRCI can efficiently capture the mixing between the Feshbach and shape resonances in dicyanoethylene isomers, which has significant consequences for their lifetimes.

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“…It is useful to group the available computational approaches into two classes according to how the embedding continuum is treated: Class one methods solve the scattering problem explicitly, while class two methods treat the continuum only implicitly and use L 2 wavefunctions. Examples for class one methods include the R-matrix and the complex Kohn method [11][12][13], examples for L 2 methods include complex absorbing potentials (CAP) [4,14], the Hazi-Taylor stabilization (HTS) method [15][16][17], and the regularized analytical continuation (RAC) method [18,19].…”

Section: Introductionmentioning

confidence: 99%

Computing resonance energies directly: method comparison for a model potential

Davis

Sommerfeld

2021

Eur. Phys. J. D

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In contrast to bound states, electronically metastable states or resonances still represent a major challenge for quantum chemistry and molecular physics. The reason lies in the embedding continuum: Bound states represent a many-body problem, while resonances represent a simultaneous scattering and many-body problem. Here we focus on so-called L 2 -methods, which treat the continuum only implicitly, but rather take the 'decaying state' perspective and emphasize electron correlation in the decaying state. These methods represent a natural extension of quantum chemistry into the metastable domain and are suitable for, say, modeling electron-induced reactions or resonant photo detachment. The three workhorse L 2methods are complex absorbing potentials, the stabilization method, and regularized analytic continuation. However, even for these three methods, making comparisons is less than straightforward as each method works best with a unique blend of electronic structure methods and basis sets. Here we address this issue by considering a model potential. For a model, we can establish a reliable reference resonance energy by using the complex scaling method and a discrete variable representation. Then, we can study the performance of the three workhorse methods as well as effects of more approximate Gaussian basis sets.

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Electron Scattering by Small Molecules

Cited by 17 publications

References 232 publications

Recent Advances in the Study of Negative‐Ion Resonances Using Multiconfigurational Propagator and a Complex Absorbing Potential

Recent Advances in the Study of Negative‐Ion Resonances Using Multiconfigurational Propagator and a Complex Absorbing Potential

Projected Complex Absorbing Potential Multireference Configuration Interaction Approach for Shape and Feshbach Resonances

Computing resonance energies directly: method comparison for a model potential

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