I wrote that - is a constant a Gaussian? Anyway that is how I got 5 -
and it is the
9-parameter Cromer-Mann approximation..
And Yes - each component is added to the B value to build up the real space
atomic density.
as you show.
Eleanor
Bernhard Rupp wrote:
Dear All,
I read in SFALL docu that a "2- or 5-Gaussian"
approximation for SFs is used - I quote from SFALL docu:
begin----------------------------------------------------------------
a1*exp(-b1*s*s) + a2*exp(-b2*s*s) - 2 Gaussian approximation
(Agarwal, 1978)
or as:
a1*exp(-b1*s*s) + a2*exp(-b2*s*s) + a3*exp(-b3*s*s)
+ a4*exp(-b4*s*s) + c
- 5 Gaussian approximation
-------------------------------------------------------------------end
Note:
1) The second formula is a 4, not 5 Gaussian approximation -
Is it the 9-parameter Cromer-Mann approximation?
2) If so, one would need to convert this (reciprocal space) scattering
function into real space e-density when making the map to be FFTed:
rho(r) -> FT -> f(s) <-this f(s) is what the scattering formula above
describes
for example from
recip: exp(-Bs*s/4) I would get FT-1 -> real:
((4pi/B)**3/2)exp(-4pi**2*r**2/B)
and use that actually to decribe the atom shape in the map generation. True?
Thx,
br
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Bernhard Rupp
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