The reliability of the Maximum Entropy Method (MEM) to reconstruct finite temperature electron density (ED) is here discussed, investigating the case of periclase (MgO). A theoretical electron density has been generated by quantum mechanic calculations and folded with a function simulating atomic thermal motion, in order to produce a reference errorless ED [rho(r)(REF)]. The Fourier coefficients of p(r)(REF) have been calculated, and used as "observed" diffraction intensities to reconstruct via MEM the original ED. The electron density attained by MEM [rho(r)(MEM)] and rho(r)(REF) have been compared with each other (pixel-by-pixel and critical points) to assess the ability of MEM to retrieve EDs, on the basis of a set of observed structure factors. We have carried out our study varying the number of observed structure factors [i.e. sin (theta)/lambda cut-off], the nature of the prior-density [uniform density and procrystal-like model] and the way in which the prior-density is treated during MEM maximization [fixed or free to change]. We observe that (i) it is recommendable to use the prior-density as a start point only, and allow it to change during maximization; (ii) the closer is the prior-density to p(r)REF, the easier one attains by MEM a correct ED; (iii) if the prior-density is varied and a sufficient large number of observed structure factors used, then MEM tends to yield converging EDs, regardless of the prior-density chosen as a start point.
About the reliability of the Maximum Entropy Method in reconstructing electron density : the case of MgO / M. Merli, A. Pavese. - In: ZEITSCHRIFT FUR KRISTALLOGRAPHIE. - ISSN 0044-2968. - 221:9(2006), pp. 613-620.
|Titolo:||About the reliability of the Maximum Entropy Method in reconstructing electron density : the case of MgO|
PAVESE, ALESSANDRO (Ultimo)
|Parole Chiave:||Electron density; Maximum Entropy Method; MEM; MgO; Periclase|
|Settore Scientifico Disciplinare:||Settore GEO/06 - Mineralogia|
|Data di pubblicazione:||2006|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1524/zkri.2006.221.9.613|
|Appare nelle tipologie:||01 - Articolo su periodico|