Flow diagram for EPSR
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EPSR addresses the problem of calculating a three-dimensional structure exploiting the information contained in diffraction data.
What is EPSR?
EPSR is a computational technique addressing the problem of calculating a three-dimensional structure exploiting the information contained in diffraction data.
EPSR iterates a direct Monte Carlo simulation of a molecular system, correcting the pair interaction potential between molecules at each stage of the iteration by comparison with the diffraction data sets. (see attached flow diagram to the right of this page)
To download the latest version of the EPSR software please use this link: http://disordmat.moonfruit.com/
Learn how to use EPSR by following the tutorial material produced for the Data Analysis workshop 2010 (please remember that this tutorial now refers to a previous version of EPSR so some features might be outdated).
It is well known however that whereas there are many computer simulations of a wide range of liquids available in the literature using many different intermolecular potentials, it is extremely unusual for those simulations to reproduce g(r) quantitatively (...).
This is especially true in the case of water (...). Yet on the experimental side the number of groups worldwide who are attempting to measure structure of water via the site-site radial distribution functions can probably be counted on the fingers of one hand.
It is not surprising therefore that the few experimental determinations of water that do exist are not in total agreement with each other, but it certainly is remarkable thatnone of the simulation work to date is in full quantitative agreement with any of the available diffraction data. (...) modern models of water give a qualitative description of water structure at ambient conditions, but quantitative discrepancies remain and become larger as the temperature and the pressure are raised." (Soper A K 1998 J. Mol. Liq. 78 179-200)
Useful EPSR references by A.K.Soper:
• 2007 J. Phys.: Condens. Matter19 No 41, 415108 (15pp), On the uniqueness of structure extracted from diffraction experiments on liquids and glasses, http://dx.doi.org/10.1088/0953-8984/19/41/415108
• 2007 J. Phys.: Condens. Matter19 No 33, 335206 (18pp), Joint structure refinement of x-ray and neutron diffraction data on disordered materials: application to liquid water, http://dx.doi.org/10.1088/0953-8984/19/33/335206
• 2005 Phys. Rev. B 72, 104204 Partial structure factors from disordered materials diffraction data: An approach using empirical potential structure refinement, http://dx.doi.org/10.1103/PhysRevB.72.104204
• 2001 Mol. Phys. 99 no.17 1503-1516, Tests of the empirical potential structure refinement method and a new method of application to neutron diffraction data on water http://dx.doi.org/10.1080/00268970110056889
• 2000 Chem. Phys. 258, 121-137, The radial distribution functions of water and ice from 220 to 673 K and at pressures up to 400 MPa, http://dx.doi.org/10.1016/S0301-0104(00)00179-8
• 1998 J. Mol. Liquids 78, Issue 3, 179-200, Determination of the orientational pair correlation function of a molecular liquid from diffraction data, http://dx.doi.org/10.1016/S0167-7322(98)00091-9
• 1996 Chem. Phys. 202, Issues 2-3, 295-306, Empirical potential Monte Carlo simulation of fluid structure http://dx.doi.org/10.1016/0301-0104(95)00357-6
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