def SetDefaultREFDModel():
    """Fills in default items for the REFD Models dictionary which are 
    defined as follows for each layer:
    
    * Name: name of substance
    * Thick: thickness of layer in Angstroms (not present for top & bottom layers)
    * Rough: upper surface roughness for layer (not present for toplayer)
    * Penetration: mixing of layer substance into layer above-is this needed?
    * DenMul: multiplier for layer scattering density (default = 1.0)
        
    Top layer defaults to vacuum (or air/any gas); can be substituted for some other substance.
    
    Bottom layer default: infinitely thisck Silicon; can be substituted for some other substance.
    """
    return {'Layers': [{'Name': 'vacuum', 'DenMul': [1.0, False]}, {'Name':
        'vacuum', 'Rough': [0.0, False], 'Penetration': [0.0, False],
        'DenMul': [1.0, False]}], 'Scale': [1.0, False], 'FltBack': [0.0, 
        False], 'Zero': 'Top', 'dQ type': 'None', 'Layer Seq': [],
        'Minimizer': 'LMLS', 'Resolution': [0.0, 'Const dq/q'], 'Recomb': 
        0.5, 'Toler': 0.5, 'DualFitFiles': [''], 'DualFltBacks': [[0.0, 
        False]], 'DualScales': [[1.0, False]]}
