An independent, general method for checking consistency between diffraction data and partial radial distribution functions derived from them: the example of liquid water

Abstract

There are various routes for deriving partial radial distribution functions of disordered systems from experimental diffraction (and/or EXAFS) data. Due to limitations and errors of experimental data, as well as to imperfections of the evaluation procedures, it is of primary importance to confirm that the end result (partial radial distribution functions) and the primary information (diffraction data) are consistent with each other. We introduce a simple approach, based on Reverse Monte Carlo modelling, that is capable of assessing this dilemma. As a demonstration, we use the most frequently cited set of "experimental" partial radial distribution functions on liquid water and investigate whether the 3 partials (O-O, O-H and H-H) are consistent with the total structure factor of pure liquid D 2 O from neutron diffraction and that of H 2 O from X-ray diffraction. We find that while neutron diffraction on heavy water is in full agreement with all the 3 partials, the addition of X-ray diffraction data clearly shows problems with the O-O partial radial distribution function. We suggest that the approach introduced here may also be used to establish whether partial radial distribution functions obtained from statistical theories of the liquid state are consistent with the measured structure factors.

The structure of liquid water beyond the first hydration shell

“…The simulations were carried out using Gromacs 22 on the TIP4P/2005 23 force field as in a previous publication on the structure of water 11 . This particular model for water was chosen since it is known to be the best available to describe the structural properties of liquid water when compared with many other water models [24][25][26] . It is also the best model to reproduce many other experimental quantities 23 at ambient conditions such as density, isothermal compressibility, thermal expansion coefficient, heat capacity at constant pressure, heat of vaporization, static dielectric constant, self-diffusion coefficient and the melting temperature.…”

Reverse Monte Carlo investigations concerning recent isotopic substitution neutron diffraction data on liquid water

“…The method is also suitable for establishing whether various input data sets are consistent with each other: if they are then they can be fitted simultaneously within their uncertainties [34]. If, on the other hand, not each element of the input set is consistent with the others then it is possible to tell which element is problematic: an approach proposed and tested recently [41] for input data consisting of TSSF-s and PRDF-s is applied in this work.…”

Számítógépes modellezési vizsgálatok a tiszta víz szerkezetvizsgálatával kapcsolatban: a kölcsönhatási potenciálok és a mért diffrakciós adatok közötti konzisztencia kérdése

“…Ez a tény ismételten rávilágít a diffrakciós kísérletekkel kapcsolatban mind a mai napig létező problémákra. A fenti témakörhöz kötődően azt is megmutattuk, hogy az említett "kísérleti" PPKF-eket a dolgozatban felhasznált egyik röntgendiffrakciós [Fu 2009] és a neutrondiffrakciós [Soper 1997] TSSSF-fel együtt RMC modellezve mindkét mérési adattal tökéletes egyezés érhető el, miközben az O-O "kísérleti" PPKF-fel való egyezés érzékelhetően romlik ahhoz a számításhoz képest, amikor csak a neutrondiffrakciós adattal való konzisztenciát vizsgáltuk [Steinczinger 2012].…”