Surface Physics Data

• Analogous to atomic physics data.
  • follow same general format.
• Namely, for each process, have
  • A ``yield'', ``reflection coefficient'', etc.
    probability ,
  • Data specifying product(s) velocity.
  • Again, sort naturally into two internal arrays: ``yields'' & ``handling'' data.
• Original DEGAS surface physics is mostly simple.
• E.g., for reflections:
  • Reflection coefficient
    ( dependence in code itself),
  • Energy reflection coefficient R_E (E_in),
  • Reflected distribution cosine or cosine-specular.
  • minimal internal and external data.
• Adequate for many DEGAS 2 applications.

• However, may need more general
  product distributions.
• Example: Bateman format
  (Bateman 1980, Heifetz 1984).
  • For each pair , have
    conditional distribution for product atom:

    

  • Sample this from three 1-D distributions:
    • First, sample velocity v₀ from

      

    • Second, get

      

    • And, finally, from

      

• Store inverse cumulative distributions
  ,

  

  for, say, 5 values of .

• E.g., for a single of H Fe reflection,

  8.27750E-01

 
  1.99146E+00  2.25513E+00  2.32691E+00  2.36544E+00  2.40806E+00

for random number .

 
  5.16532E-01  6.99576E-01  8.11503E-01  8.99906E-01  9.67300E-01
  3.70481E-01  6.11799E-01  7.63020E-01  8.72539E-01  9.61285E-01
  3.80010E-01  6.18834E-01  7.63825E-01  8.75375E-01  9.61256E-01
  3.57688E-01  5.95520E-01  7.51752E-01  8.59766E-01  9.57489E-01
  3.48497E-01  5.17881E-01  6.53833E-01  7.79846E-01  9.23956E-01

for random numbers .

And

 -9.54674E-01 -5.93616E-01 -4.55439E-03  6.11607E-01  9.54292E-01
 -9.39719E-01 -5.34726E-01  7.70975E-02  5.91124E-01  9.38723E-01
 -9.47749E-01 -5.99118E-01 -5.34413E-03  5.58645E-01  9.59176E-01
 -9.52932E-01 -5.09963E-01  1.11845E-01  6.68895E-01  9.59592E-01
 -9.63812E-01 -6.32861E-01  2.84474E-02  6.49311E-01  9.65024E-01

 -9.49486E-01 -5.27460E-01  4.71202E-02  5.40823E-01  9.43092E-01
 -9.18789E-01 -5.34890E-01  3.87104E-03  5.97719E-01  9.43635E-01
 -9.35546E-01 -5.66353E-01 -6.17420E-02  5.65376E-01  9.28863E-01
 -9.39133E-01 -5.88361E-01  4.03247E-02  5.36441E-01  9.41553E-01
 -9.42917E-01 -5.66390E-01  4.88304E-03  5.72368E-01  9.58254E-01

 -9.59566E-01 -6.35221E-01 -7.50576E-02  5.72627E-01  9.59374E-01
 -9.43053E-01 -6.23133E-01 -8.35145E-02  5.13894E-01  9.33565E-01
 -9.42753E-01 -6.40605E-01 -1.50300E-02  5.51493E-01  9.32335E-01
 -9.28625E-01 -5.03451E-01  3.69856E-02  6.04412E-01  9.51354E-01
 -9.47567E-01 -5.75171E-01  6.78900E-02  6.17675E-01  9.61149E-01

 -9.42125E-01 -6.25972E-01 -6.74072E-02  5.10579E-01  9.26111E-01
 -9.24288E-01 -5.62514E-01 -6.67559E-02  5.49679E-01  9.57450E-01
 -9.45958E-01 -5.88903E-01  6.07203E-02  5.98492E-01  9.45981E-01
 -9.64714E-01 -6.17340E-01 -2.49212E-02  5.61052E-01  9.49261E-01
 -9.59291E-01 -6.47473E-01 -8.40439E-02  4.58677E-01  9.33637E-01

 -9.43142E-01 -5.25077E-01  4.79891E-02  6.22436E-01  9.53027E-01
 -9.43214E-01 -5.90395E-01  2.32011E-02  5.42675E-01  9.35411E-01
 -9.40994E-01 -4.99927E-01  7.81558E-02  6.19613E-01  9.44418E-01
 -9.35018E-01 -5.38589E-01  8.60652E-02  6.47157E-01  9.51505E-01
 -9.49873E-01 -5.38587E-01  8.93784E-02  6.39298E-01  9.66431E-01

for random number .

• Summarize contents of each data file:
  1. ,
  2. ,
  3. ,
  4. ,
• All stored as 1-D array in external file,
  • Array behavior provided by macros.
• Existing data from Marlowe code on
  nonuniformly spaced energy grid.
  • arrays of independent variables
    stored explicitly,
  • Extra step required in interpolation
    to search for closest index.
• In code, R_N data funneled into ``yield'' array,
• F's stored in ``handling'' array.
  • 7-D array stored as 1-D!
  • Essential for efficiency since array is very ``ragged''.
• Treat random numbers as ``independent variables''
  F's can be interpolated like any other table!

• With both elastic scattering & Bateman format data:
  • Able to handle ``new'' data formats easily,
  • Should retrofit reaction data to match
    PMI data format.