James, > nearBragg2D does not contain a random number generator. I made the atom > constellations for my DS calculations using an awk script.
My point was that your 'constellation of points' has to be some kind of random sampling since it has to be a sampling both over the lattice and over time, with some assumed model for the lattice and time variations in the atomic positions. Most importantly if we are to simulate the effects of DS, we must also have a model for the correlations of the displacements of the atoms from their mean positions over the lattice and over time. > I would > appreciate it if you could create a constellation of atoms > that has the > "correlated displacements" you are talking about, so that I > (and others) > can test your hypothesis with my program. What you're asking for is completely unrealistic for a number of reasons, for one I haven't worked on DS for 10 years, I don't have access to the necessary software any longer and I certainly don't have the time to write DS simulation software now. However the most cogent reason is that correlated displacements clearly cannot be represented by a single constellation of points. A single constellation can only represent the PDF of the instantaneous density w.r.t. the displacements. For the correlated displacements we need the joint PDF over the lattice and over time. For even the most naïve simulation of the acoustic DS we would need the density sampled over a representative 'crystal', say at least 10 unit cells in each direction in order to be able to simulate the effect of the lattice correlations, multiplied by a sufficient sampling over time to give a statistically meaningful result for the effect of the time correlations. For these reasons IMO a simulation of either the average or the instantaneous atomic distribution that you are proposing is not a sensible way to approach this problem. In fact the necessary equations for the various components of the average intensity directly in terms of the structure factors are published: to get the answer to your question all you need to do is look them up. If you can't locate them easily, I can probably dig them out from my old lecture notes. Just give me a while to find and organise them. Cheers -- Ian Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing i.tic...@astex-therapeutics.com and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
