[ccp4bb] atomic FF used in SFALL

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CCP4bb <-- 2007 <-- October 2007 <-- 10 October 2007

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From: John Bruning jbruning {- at -} SCRIPPS {- dot -} EDU
Date: 2007-10-10

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Date: 2007-10-10

Subject: atomic FF used in SFALL
From: Bernhard Rupp bernhardrupp {- at -} SBCGLOBAL {- dot -} NET
Date: 2007-10-10

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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CCP4bb navigation

CCP4bb <-- 2007 <-- October 2007 <-- 10 October 2007

Previous message:
Subject: easy way to make alternate conformers?
From: John Bruning jbruning {- at -} SCRIPPS {- dot -} EDU
Date: 2007-10-10

Next message:
Subject: His tag does not bind.
From: changrui lu changrui {- at -} GMAIL {- dot -} COM
Date: 2007-10-10