[Wien] atomic form factor calculation

[HW Sheng]

Dr. Marks,

Sorry for confusing you.

When I mention the simulation of the X-ray diffraction structure factor, I
didn't mean the same method used in lapw3. Actually I did a large scale MD
of millions of atoms, where I also desire to have an accurate estimate of
the atomic form factors of different species.

Hope this will clarify things.

Howard

>-----Original Message-----
>From: L. D. Marks [mailto:L-marks at northwestern.edu]
>Sent: Wednesday, April 26, 2006 8:48 AM
>To: HW Sheng
>Subject: RE: [Wien] atomic form factor calculation
>
>
>What is it you really want:
>a) Atomic scattering factors with bonding effects?
>b) A value for <f^2>?
>
>If you do not need a), just calculate <f^2> (in real or reciprocal space
>as appropriate) by a convolution and/or FFT->Multiply->FFT.
>
>On Wed, 26 Apr 2006, HW Sheng wrote:
>
>> Dr. Marks,
>>
>> Thanks for the paper. I have read it and it's an excellent paper.
>>
>> I understand that the chemical bonding introduces changes to the atomic
>> factor(s), due to charge redistribution and orbital
>hybridization. It's not
>> surprising that dstart generates the same atomic factor as the tabulated
>> values, since dstart basically superposes the charge densities
>of all atoms,
>> without relaxing to their electronical ground states.
>>
>> My problem still remains: how can I generate the atomic form factor of
>> individual atoms in the unit cell? In my simulation of the X-ray
>structure
>> factor (e.g. of a liquid), I need not only <f>^2, but also
><f^2>. It's the
>> latter that I found difficult to get.
>>
>> I come by a solution, but am not sure if it will work. One may
>do the Bader
>> analysis first, and the charge density can be divided into regions of
>> different atoms. The subsequent Fourier transform of the charge
>density (of
>> different atoms) then gives the atomic form factors. How do you
>think? Are
>> there other simpler workarounds?
>>
>> Thank you,
>>
>> Howard
>>
>>> -----Original Message-----
>>> From: wien-bounces at zeus.theochem.tuwien.ac.at
>>> [mailto:wien-bounces at zeus.theochem.tuwien.ac.at]On Behalf Of L. D. Marks
>>> Sent: Tuesday, April 25, 2006 10:18 PM
>>> To: A Mailing list for WIEN2k users
>>> Subject: Re: [Wien] atomic form factor calculation
>>>
>>>
>>> See http://scripts.iucr.org/cgi-bin/paper?lc5043 . The tabulated x-ray
>>> scattering factors and those from dstart are essentially the same, the
>>> changes on bonding are much larger.
>>>
>>> On Tue, 25 Apr 2006, HW Sheng wrote:
>>>
>>>> Dear Wien users,
>>>>
>>>> I wonder if I can use lapw3 to calculate the atomic form factor for
>>>> individual atoms in an alloy.
>>>>
>>>> If I understand this correctly, lapw3 computes the atomic form factor
>>>> (so-called X-ray structure factor) of a unit cell, including
>>> contributions
>>>> from all elements (if not an elemental solid) in the unit cell.
>>> The is the
>>>> averaged atomic form factor <f>. Any guidance/suggestions how to
>>> calculate
>>>> the form factor of individual atoms?  I need this in order to
>compare how
>>>> the atomic form factor in an alloy ( or a compound) differs from the
>>>> tabulated value of  "neutral atoms", and this information will
>help me to
>>>> simulate X-ray diffraction experiments with high accuracy.
>>>>
>>>> Your help would be greatly appreciated.
>>>>
>>>> Howard Sheng
>>>>
>>>> Dept. Materials Science & Engineering
>>>> Johns Hopkins University
>>>>
>>>>
>>>
>>> Note: if you have an old email address for me, please note that
>"nwu" has
>>> been changed to "northwestern".
>>> -----------------------------------------------
>>> Laurence Marks
>>> Department of Materials Science and Engineering
>>> MSE Rm 2036 Cook Hall
>>> 2225 N Campus Drive
>>> Northwestern University
>>> Evanston, IL 60208, USA
>>> Tel: (847) 491-3996 Fax: (847) 491-7820
>>> email: L-marks at northwestern dot edu
>>> http://www.numis.northwestern.edu
>>> -----------------------------------------------
>>>
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>
>Note: if you have an old email address for me, please note that "nwu" has
>been changed to "northwestern".
>-----------------------------------------------
>Laurence Marks
>Department of Materials Science and Engineering
>MSE Rm 2036 Cook Hall
>2225 N Campus Drive
>Northwestern University
>Evanston, IL 60208, USA
>Tel: (847) 491-3996 Fax: (847) 491-7820
>email: L-marks at northwestern dot edu
>http://www.numis.northwestern.edu
>-----------------------------------------------