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Electron and Photon Initiated Chemistry EPIC Workshop

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Key part of environmental chemistry and radioactive waste problem needs new trained researchers ... all the interesting plasma chemistry is electron initiated ... – PowerPoint PPT presentation

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Title: Electron and Photon Initiated Chemistry EPIC Workshop


1
Electron and Photon Initiated Chemistry(EPIC)Wor
kshop
  • Notes on Draft Outline of Report
  • and
  • Summary of Themes of the First Day

2
Notes on Report Recommendations
  • Notes taken on the morning of the second day,
    during discussion of outline of report

3
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

4
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
  • Kushners section(table of compounds)
  • Orlandos section
  • this theory effort will stimulate the renewal of
    needed experimental efforts in this area

5
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

6
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

7
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

8
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 dont converge rapidly
    enough for Rydberg excitation

9
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)

10
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

11
Summary of the Themes of the First Day of the
EPIC Workshop
12
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

13
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)

14
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

15
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

16
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 N1 electron correlation) which
    are largely solved by other modern methods for
    bound anions

17
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

18
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
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