9.25 path()

Description

Define a FEFF path and specify the path parameters. The paths defined in this way can be used in either ff2chi() or feffit() to create $\chi$(k).

Paths are referred to by an integer index, which is a required keyword. Every path must have an index and a feffnnnn.dat file associated with it - all other path parameters are optional, taking ``normal defaults'' (zero for all parameters except S02 which defaults to one).

Input Program Variables

feff_file is used as the default feffnnnn.dat file.

Keywords/Values

All values are treated as text strings except for index which must be an integer. Except for label and feff, strings for path parameters are interpreted as math expressions, either giving a scalar or array.

Keyword	Variable	Default	Description
1index			path index, an integer used to make path lists
2feff			feffnnnn.dat file to use for this path
label			text string to describe path
s02		1	NS02 - constant amplitude factor
e0			E0 - energy shift
delr			$\Delta$R - change in path distance
sigma2			$\sigma^{2}_{}$ - mean-square-displacement
third			C3 - third cumulant
fourth			C4 - fourth cumulant
ei			Ei - shift in imaginary energy term.
k_array			array of k-values for k-dependent phase-shift and amplitudes
phase_array			array of k-dependent phase-shift
amp_array			array of k-dependent amplitude factor

Output Program Variables

None.

Notes

All the numerical Path Parameters can be generalized expressions of the fitting variables and other defined Program Variables. The path() command only defines the path, and may not even cause the feffnnnn.dat file to be read.

Examples

 
  Iff> path(index = 1, file = feff0001.dat, s02= 1, 
            sigma2 = sig2)
  Iff> path(2,  feff0002.dat, s02= 1,  sigma2 = sig2)
  Iff> 
  Iff> path(3,  feff0003.dat, sigma2 = 'sig2 * sqrt(3)')
  Iff> path(3,  delr   = reff * alpha)

See also

ff2chi()(Section 9.12), feffit()(Section 9.11), get_path() (Section 9.16), Chapter 7.