Dear Liliana, of course the remarks of Maxim are correct, the experimental conditions are very important. Just additionally: Very important is also the range of d* which is covered experimentally for the accuracy of the displacement parameters. Of importance is also the mass of the atom. Heavy atoms (in a soft portential) can get really small ADP whereas for light atoms a considerable ADP should even be found at 0 K (Debye theory).
Andreas > Marilena L Viciu schrieb: > > Dear all, > > <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> > > I am refining a powder neutron data at low temperature (50K). I got some of the > thermal parameters negative although the model seems to be quite right (the data at > room temperature behaved well with the same model). From your experience, is this > the case of a wrong model? > > > > I really appreciate any comment! > > Thank you! > > Liliana -- Dr. Andreas Leineweber Max-Planck-Institut fuer Metallforschung Heisenbergstrasse 3 70569 Stuttgart Germany Tel. +49 711 689 3365 Fax. +49 711 689 3312 e-mail: [EMAIL PROTECTED] home page of department: http://www.mf.mpg.de/de/abteilungen/mittemeijer/english/index_english.htm
