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PART II - Beyond the structure of liquids: novel applications of Reverse Monte Carlo. (Structural disorder in crystals, modeling the dynamic structure factor [S(Q,w)] and (possible(?)) applications related to the I(Q) determined by small angle scattering)
Dr Laszlo Pusztai
Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary
Mon, Jun. 04th 2012, 15:30
LLB - Bât 563 p15 (Grande Salle), CEA-Saclay


The RMC method is (or rather, it may be made) more general than 'just' treating neutron and X-ray diffraction signals from liquids and amorphous materials: indeed, any experimental signal that is calculable from particle positions may be modeled 'a la RMC'. Some of the already existing algorithms will be presented here.  (1)  Crystals are more and more popular targets of 'PDF-based' methods, including RMC. There are two; slightly different, Reverse Monte Carlo approaches to tackle 'total scattering' type (as opposed to 'Bragg profile' type) data from crystalline materials: RMCProfile (developed mostly at ISIS, UK) and RMCPOW (maintained now in Budapest). Via the example of the two crystalline phases of carbon tetrabromide, CBr4, the use of RMCPOW will be demonstrated for revealing the  effects of disorder in crystals. Further examples where magnetic scattering is also present will be mentioned briefly. (2) Few years ago and RMC-based approach,  RMCt, has been devised for modeling the dynamic structure factor. The idea is to take not one but several (thousand...) simulation boxes, each representing a given  instant of time. The computer programme has been written (by Orsolya Gereben, Budapest) and it has been demonstrated to work properly on model data: this  will be shown here, too. (3) There are many possible reasons behind the appearance  of a small angle scattering (SAS) signal that may have radically different physical origins; developing a 'general' modeling technique for SAS would therefore be very difficult (most probably, impossible). An RMC-based algorithm, RMCSANS, has been realised in a computer programme (also by O. Gereben) that can tackle the  aggregation of spherical particles: elements of this approach, as well application on model data, will be presented here.

+Bonus (if anyone would be interested): real-time demonstration of running RMC (perhaps on liquid water?)

Contact : Aurore VERDIER


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