# Presentation: 178686

## Electron and Photon Initiated Chemistry(EPIC)Workshop

- Notes on Draft Outline of Report
- and
- Summary of Themes of the First Day

## Notes on Report & Recommendations

- Notes taken on the morning of the second day, during discussion of outline of report

## Outline

- I.     Executive Summary
- II.   Importance of Theoretical Simulation of
-        Electron and Photon Initiated Chemistry
- III.  New Research Opportunities
- IV.  Outline of a New National Research Program
- V.    Educational Impact of a New National Program

## II. Importance of Theoretical Simulation of Electron and Photon Initiated Chemistry

- [*Motivation and Impact why is it important to understand all this*]
- Introduction-- what are the processes (table of reactions), techniques applicable to atmospheric chemistry + other areas as well
- Kushner’s section(table of compounds)
- Orlando’s section
- this theory effort will stimulate the renewal of needed experimental efforts in this area

## III. New Research Opportunities

- Why now ?
- Advances in electronic structure theory -- electron affinities
- Advances in computing power, need for Terascale computing, AND structure codes run there already
- Advances in electron scattering -- Multichannel electron excitation calculations on polyatomics
- can address some critical problems (specific cross sections) needed for models quickly, [scale up of existing CI based methods] (get immediate examples from Kushner)
- Experimental efforts in U.S. are closing down
- Many quantities are difficult to address experimentally, ALSO the time scale for getting results experimentally is much longer, computational approach is more economical

## III. New Research Opportunities (Cont)

- What can we do right now, with current methods ?
- Simplest description of elastic scattering
- electronic excitation with simple target states
- limitations
- methods for e-atom
- Investment now can leverage existing methods and computational platforms to make immediate impact (on both Plasma Proc.  and environmental chem.  Brings credibility for further effort.
- Benchmarking against experimental measurements

## III. New Research Opportunities (Cont)

- What requires major future investment ?
- E.g. Branching ratios and dynamics of highly excited molecules
- accurate excitation cross sections
- cross sections for processes in condensed phases and interfaces
- ionization (especially of excited states)
- electron transport phenomena (vibrational excitation of polyatomics)
- identification of etchants for new materials
- timeline for progression of molecules or problems

## IV.  Outline of a New National Research Program

*[national coordinated effort, codes on common software platform etc**.]*
- Issues associated with electron transport (Rescigno)
- incorporate quantum chemistry advances into electron scattering (elastic, momentum transfer, vib excit)
- Electronic excitation (Tennyson)
-  The intermediate energy problem
- close coupling expansions don’t converge rapidly enough for Rydberg excitation

## IV.  Outline of a New National Research Program (Cont)

- Dissociation
- electron impact dissociation
- excited state potential surfaces (inc. triplets)
- post collision dynamics
- dissociative attachment and recombination
- area where quantum chemistry can have immediate impact stabilization, complex rotation, etc. for resonance states.
- Ionization
- electron impact ionization of molecules and excited states of atoms (total cross sections are easy to measure and semiclassical formulas work well)

## V.  Educational Impact of a New National Program

- Need for new researchers in this field
- Key part of environmental chemistry and radioactive waste problem needs new trained researchers
- Training in this field prepares students in physical science and computational science to solve other important problems
- Raising skills level in scientific MPP computing

## Summary of the Themes of the First Day of the EPIC Workshop

## Themes of the First Day of the EPIC Workshop

- Funding Opportunity
- Possible Federal initiative in computational science (SS*?) (what can you do with 1-100 Tflops)
- New initiative will be joint between NSF and DOE
- Ongoing realignment of DOE program in atomic physics
- Possibility of making major impact in plasma processing and waste remediation

## Plasma Processing

- all the interesting plasma chemistry is electron initiated
- quantitative understanding for most of the interesting process gases and relevant fragments is sparse -- specific examples
- branching ratios for electron-impact dissociation are prominently absent: identifying the species
- abatement of PFCs in burn boxes is a plasma dependent process, as is chamber cleaning
- ionized metal plasma vapor deposition is key for new interconnect in microprocessors (e-M* ionization)
- theory and advanced computational modeling can have a definitive economic impact (LSI example)

## Waste Remediation (Chemistry in extreme environments)

- Gas production in mixed chemical radioactive waste largely driven by secondary electron cascades
- Low T plasma destruction of undesirable compounds
- Low T plasma remediation of NOx
- Dissociative Attachment branching ratios are key
- Differences between gas phase processes and processes on surfaces or in liquids
- No absolute cross sections at interfaces are available.  Coupling of energy from solid to the adsorbates
- Electron -H2O collisions play key role

## State of computational theory for electron dynamics

- Simple calculations (single configuration targets) for elastic and electronic excitation on polyatomics can have important impact
- Even the simplest calculations on large polyatomics (e.g. c-C4F8) require development of scalable portable algorithms for massively parallel computing
- branching ratios are currently not computable even for simplest polyatomics of interest.  Internal conversion of energy after excitation, triplet excitation, THIS is what you need 100 TFLOPs for, and this is the quant chem + electron dyn. + nuclear motion.
- formalisms use integrals involving continuum functions (not conventional objects of modern quantum chemistry)
- All current (continuum) theory based on CI , needs contracted CI and  flexible choice of configurations

## State of the Relevant Quantum Chemical Art

- For ground states it is meaningless to try to evaluate accuracy of methods without a systematic study of basis set convergence. For ground states the basis set problem is solved for 1st and 2nd and main group 3rd row
- Methods for electronically excited states all scale poorly
- multireference CI (prohibitively expensive for large systems)
- multireference perturbation theory (convergence is still open question)
- coupled cluster methods (promising but still demanding)
- basis sets still are a problem for non-valence excited states
- spin orbit coupling will be important, and nonadiabatic coupling also
- Electron affinity calculations by CI share many of the difficulties of electron scattering (balancing N & N+1 electron correlation) which are largely solved by other modern methods for bound anions

## Interface between Quantum Chemistry and Electron Dynamics

- Current structure codes have flexible modular construction but are missing key elements of electron scattering calculations
- continuum integrals
- sufficiently flexible configuration selection (contracted CI also necessary)
- complex-valued orbitals
- technology exists for calculating non-adiabatic couplings which are not in many widely-used codes
- Simplest methods for electron-polyatomic scattering (1 config targets) could be coded inside modern structure codes

## Interface between Quantum Chemistry and Electron Dynamics (cont)

- Putting electron continuum in structure codes opens opportunities for new formalisms based on
-  EOM CC (calculates directly differences in energy)
- Greens fcn propagator and MBPT methods
- Attacking problem of collisions with molecules in condensed media can then leverage work in electronic structure of solutes
- Not sensible to build new electron scattering formalisms outside of quantum chemistry codes
- Are benchmark systems  important (H2O good theory benchmark? A fragment or radical?) ???
- Direct evaluation of summed or average dynamical quantities e.g. rate constants?
- Electron-ion dissociative recombination