Ok - sorry, changed degrees into radians. But there is still a difference for sulphur in aluminite.
Best regards, Luke K. > OK, here it goes: > > Uiso = 1/3 * [U22 + 1/sin^2(beta)*(U11 + U33 + 2U13cos(beta)] = > 1/3 * [0.01562 + (1/sin^2(110.18))*(0.01937 + 0.01277 + 2* > (-0.00027)*cos(110.18)] = > 1/3 * [0.01562 + (1/(0.9386)^2) * (0.03214 + (-0.00054)*(-0.345)] = > 1/3 * [0.01562 + (1/0.88097) * 0.0323263] = > 1/3 * [0.01562 + 1.135 * 0.0323263] = > 1/3 * (0.01562 + 0.03669) = 1/3 * 0.05231 = 0.01726 > > The given Uiso for sulphur is, meanwhile, 0.01621. > > I have also been trying to calculate Uiso for melanophlogite, which is > cubic, co the formula goes: > > Uiso = 1/3* (U11 + U22 + U33). > > Using this formula, I have obtained the value of 0.0339, which is exactly > the same as the one given in the corresponding CIF file. > However, calculating the Uiso using the GENERAL formula gives the value of > 0.0287. Both values (0.0339 and 0.0287) were calculated using an EXCEL > spread sheet. So how is such a difference possible? > > Best regards! > > Luke Kruszewski > > >> Dear Łukasz, >> >> There must be something wrong with your calculation. A quick examination >> shows that S must have a higher displacement parameter than Al and that >> Ueq must be approximately 0.016. >> >> I hope this helps. >> >> Bob Gould >> >> >> On 10/02/2014 21:50, "Łukasz Kruszewski" wrote: >>> Dear Rietveld friends, >>> >>> I'm having some problems with calculating Uiso from the anisotropic >>> parameters. Here is an example - I copy first two sites of aluminite >>> (monoclinic): >>> >>> _atom_site_aniso_label >>> _atom_site_aniso_U_11 >>> _atom_site_aniso_U_22 >>> _atom_site_aniso_U_33 >>> _atom_site_aniso_U_12 >>> _atom_site_aniso_U_13 >>> _atom_site_aniso_U_23 >>> S 0.01937 0.01562 0.01277 -0.00248 -0.00027 0.00954 >>> Al1 0.01117 0.01169 0.01295 0.00006 -0.00012 0.00789 >>> >>> Using the formula for Uiso for the monoclinic system, which is: >>> >>> >>> 1/3 * [U22 + 1/sin^2(beta)*(U11 + U33 + 2U13cos(beta)] >>> >>> for the "S" site we obtain the value of 0,0054 >>> >>> for "Al": 0.01225 >>> >>> Meanwhile, the listed Uiso are: >>> >>> _atom_site_label >>> _atom_site_fract_x >>> _atom_site_fract_y >>> _atom_site_fract_z >>> _atom_site_U_iso_or_equiv >>> S 0.70076 0.37376 0.93018 0.01621 >>> Al1 0.65581 0.45332 0.47633 0.01229 >>> >>> While the author-given value for Al is close to the one calculated >>> myself, >>> the one for S is much different. By the way, 0.01621 * 1/3 = 0.0054. >>> >>> I could find it a simple mistake, I've found such a problem in case of >>> many other structures. And here's my kind question: am I missing >>> something? >>> >>> Best regards! >>> >> >> >> -- >> Robert Gould >> Tel.UK: +44 (0)131 667 7230 or +44 (0)796 040 3872 >> Canada: +1 519 387 8223 >> >> >> --- >> This email is free from viruses and malware because avast! Antivirus >> protection is active. >> http://www.avast.com >> >> > > > -- Łukasz Kruszewski, Ph.D., adjunct Polish Academy of Sciences Institute of Geological Sciences X-Ray Diffraction Laboratory (coordinator) Twarda 51/55 str. 00-818 Warsaw Poland
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
