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SZFI SeminarProf. Andrea Di CiccoPhysics Division, University of Camerino 
(Italy) (host: Pusztai László)Advances in modelling X-ray absorption 
spectroscopy by reverse Monte CarloThursday, 1 December 2022, 10:00, KFKI 
Campus, Bldg. 1, 2nd floor, Conference RoomModern extended X-ray absorption 
fine structure (EXAFS) analysis is based on multiple-scattering calculations. 
Those calculations are carried out for fixed atomic configurations and proper 
account of the thermal and static disorder, corresponding to well-defined 
pair and higher-order distribution functions, can be obtained using different 
methods. The application of the Reverse Monte Carlo (RMC) method[1] is able 
to provide tridimensional models of the atomic structure compatible with a 
given set of experimental data, producing useful and consistent structural 
models. This method has been proposed and applied also to EXAFS data by 
several authors in the last 25 years and has been fully implemented in the 
framework of the RMC-GnXAS method for EXAFS data-analysis [2-7] and applied 
mainly to liquid and molecular systems. Here we present the extension and 
application of this method to multiple-edge studies of molecules, crystalline 
solids and liquids, including the long-range constraints provided by other 
techniques (e.g. diffraction). The potential and possible weaknesses of the 
RMC method are discussed, as well as the importance of accounting for the 
effect of noise levels in XAFS data. Results of RMC refinements are reported 
for several exemplary cases including Br2 and GeI4 molecular gases, 
crystalline Ge and AgBr, amorphous Ge and liquid AgBr. Those applications 
show the general interest for this method, and the importance of combining 
multiple set of data for improving the accuracy of the structural refinement 
both at short and long range. [1] R. L. McGreevy and L. Pusztai, Mol. Sim., 
1988, 1, 359–367.[2] http://gnxas.unicam.it official GnXAS website.[3] A. Di 
Cicco, A. Trapananti, S. Faggioni, and A. Filipponi, "Is there icosahedral 
ordering in liquid and undercooled metals?", Phys. Rev. Letters 91, 135505 
(2003)[4] A. Di Cicco, and A. Trapananti, "Reverse Monte Carlo refinement of 
molecular and condensed systems by x-ray absorption spectroscopy", J. Phys. 
Condens. Matter 17 S135 (2005).[5] A. Di Cicco, F. Iesari, S. De Panfilis, M. 
Celino, S. Giusepponi, A. Filipponi, Local fivefold symmetry in liquid and 
undercooled Ni probed by x-ray absorption spectroscopy and computer 
simulations, Physical Review B rapid comm. 89, 060102 (2014).[6] A. Di Cicco, 
F. Iesari, A. Trapananti, P. D'Angelo, A. Filipponi, "Structure and atomic 
correlations in molecular systems probed by XAS reverse Monte Carlo 
refinement", J. Chem. Phys. 148, 094307 (2018).[7] A. Di Cicco and F. Iesari, 
Physical Chemistry Chemical Physics, 24, 6988-7000 (2022).Join Zoom 
Meetinghttps://wigner-hu.zoom.us/j/81415140766?pwd=YWVWR1RBZkY3STlWTC9ibWxtMWtZZz09Meeting
 ID: 814 1514 0766Passcode: 569885 Minden érdeklődőt szívesen látunk! - 
Everyone is welcome to attend.Attila Nagysem-admin AT szfki.hu