Information in Atom Program
Dear all, Has anyone ever used the atom programto design crystallographic or magnetic structure? I have a difficulty at this time in the way we define the octahedra or tetrhedra in a crystallographic structure.Also I would like some advise upon how we can define a specific number of atoms or else how we can design only one unit cell in a structure. Moreover regarding the magnetic structure is there a possibility to draw the moment's vectors? Provided that the answer on the above questions is very extensive I would be very grateful if someone couldprovide me a reference to look at. Many thanks in advance, Irini
RE: Debye Temperature Lattice Thermal Expansion
This is to answer the question from Alexandros: The simplest approximation to the thermal expansion coefficient uses the Debye or Einstein specific heat through the so-called Gruneisen formula alpha=gamma*cv/(3*B*Vm) where alpha is the linear expansion coefficient (1/3 of the volume TEC), B is the Bulk modulus, cv is the lattice specific heat, Vm is the molar volume and gamma is the Gruneisen coefficient. Note that the high-temperature limit for both the Debye and Einstein formulas (cfr. Ashcroft Mermin, chapter 23) is cv-3*n*Kb, where n is the number of atoms in a molecule and Kb is the Boltzmann constant (8.31 J/mol/K). For oxides with the perovskite structure, B~150-180 GPa, Vm~3x10^-5 m^3/mol and n=5, so alpha-gamma*7x10^-6 at high temperatures. Typical values of gamma are of the order of 2. The problem with using this formula to extract the Debye temperature (thetad) from thermal expansion data is that it invariably yields irrealistically low values of Thetad. The reason of this is that gamma is an anharmonicity coefficient, which is not the same for different phonons. So, strictly speaking, one gets an anharmonicity-weighted Debye temperature. This problem has been addressed for alkali halides and perovskites in a useful paper by H. Inaba (J. Cer. Soc. Japan, 106, 1988, p 272), which also contains references to other materials. Inaba proposes a semi-empirical model which works well for non-pathological systems, and (in principle) should allow one to extract the true Debye temperature. In practice, I think this is more useful when Thetad is known and one wants to fit the TE data. By the way, getting Debye tempeatures from Debye-Waller factors is also risky, because one gets a complicated average over the phonons that project on that particulat site and direction. Paolo
what diffractometer
Dear All, we are planning to purchase a new diffractometer, which will be mostly devoted (but not exclusively) to structure determination. We will mainly study organometallic compounds and silicate minerals, working both in transmission and reflection geometry. Two possible choices for Siemens D8 equipment maybe VARIO (focusing primary monochromator) and Gobel mirror systems, both of which seem rather promising. What is your experience on these systems? Did you experience other diffractometers with similar capabilities from other companies? Replies will be warmly welcome. Thanks for your attention Natale Perchiazzi § dr Natale Perchiazzi Dipartimento di Scienze della Terra Università degli Studi di Pisa Via S.Maria 53, I-56126 Pisa tel +39 050 847269 fax +39 050 500932 e-mail [EMAIL PROTECTED] §
Re: Information in Atom Program
Dear Irini, do you mean the program ATOMS by Eric Dowty? Defining polyhedra in ATOMS is pretty straight forward by using Input1/Polyhedra (I am referring to version 5.0). Defining the no. of atoms or the size of the structure fragment drawn is done in Input1/Boundary. If you want to draw different polyhedra for identical cations then it would be easiest to just change the type of atoms. The inbuilt manual will help you in any other questions. Uwe Dr. Uwe Kolitsch Institut für Mineralogie und Kristallographie Geozentrum Universität Wien Althanstr. 14 A-1090 Wien Austria Tel +43-1-4277-53239 Fax +43-1-4277-9532 e-mail: [EMAIL PROTECTED] home page: http://www.univie.ac.at/mineralogie/kolitsch.htm
Error sum file by fullprof!!
Hi all!! I wonderwhether someone could tell me why the fullprof creates such a sum file which can not be read. Is it possible to tell me someone why this is so?many thanks in advanceIrini 2kb.sum
RE: Error sum file by fullprof!!
Hi Irini, This sum file can be read - just open it using notepad if you're in windows. I'm not certain what you'd use to read it in other OS. Jude :-) All I really need is love, but a little chocolate now and then doesn't hurt! Lucy Van Pelt (in Peanuts, by Charles M. Schulz) Dr Judith Dann R3, ISIS, RAL, Chilton, Didcot, Oxfordshire, OX11 0QX tel: (01235) 445792, fax: (01235) 445720 -Original Message- From: Mastoraki Eirini [mailto:[EMAIL PROTECTED]] Sent: 05 July 2001 13:56 To: [EMAIL PROTECTED] Subject: Error sum file by fullprof!! Hi all!! I wonder whether someone could tell me why the fullprof creates such a sum file which can not be read. Is it possible to tell me someone why this is so? many thanks in advance Irini
Re: Error sum file by fullprof!!
Actually, under Win2000k the files can be easily opened by any text editor. Waht kind of editor or OS are you using? Regards, leonardo ___ eng. Leonardo ContDpt. Materials EngineeringUniversity of Trento38050 TRENTO - ITALY Office: +39 0461 882414E-mail: [EMAIL PROTECTED]Web: http://www.ing.unitn.it/~contl "We don't need faster computers. We need better ideas." [A. Chorin, Berkeley, '00] "Sono rospo...e ho detto tutto!" [M. Neri, Berkeley, '00]___
RE: what diffractometer
Natale (and others!) We have a very new D8 equipped with dual Goebel mirrors (40mm primary and secondary), but have no experience with the Vario monochromator (very fiddly to keep well aligned so I'm told). We've just used the reflection geometry so far, as we haven't even got around to mounting the capilliary holder yet. Therefore these are observations from a short period of use. With regard to structure determination and use of the Goebel mirrors there are some things to be noted. The Bruker field personnel have very little experience with installing and aligning the diffracted beam mirror (i.e. I did it myself - not too difficult though once you've worked it out, but much patience required). I understand that the situation in Europe isn't much better. However with a mirror system it is desirable to have the second mirror to regain some of the resolution lost with just the primary one, as well as increased intensities over the alternative flat LiF or graphite monchromators, whilst also removing fluoresence. Despite the increased resolution it is still not as good as the D8 Bragg-Brentano setup, but better than the old Scintag we had. Now it is set up I am extremely satisfied with it - user errors in sample preparation with regard to displacement are not an issue, making it a potentially very good general user instrument as well as with high temperature furnaces. The mirrors do not remove Ka2, so if this is a requirement they are not suitable. One thing which is very apparent with the 660 LaB6 standard, but not so much with actual samples, is significant axial divergence (even with the supplied Soller slits), which means care needs to be taken with regard to peak profiles. I have successfully refined some simple structures using GSAS and Topas so it's not a major problem. I would imagine that most of my observations will hold true for mirror systems from other manufacturers as the geometry is basically the same. Best regards Pam Whitfield Dr Pamela Whitfield CChem MRSC Energy Materials Group ICPET Building M12 National Research Council Montreal Road Ottawa ON K1A 0R6 Canada Tel: (613) 991-2435 / (613) 998-8462 Fax: (613) 991-2384 Email: [EMAIL PROTECTED] -Original Message- From: Natale Perchiazzi [mailto:[EMAIL PROTECTED]] Sent: July 5, 2001 6:19 AM To: [EMAIL PROTECTED] Subject: what diffractometer Dear All, we are planning to purchase a new diffractometer, which will be mostly devoted (but not exclusively) to structure determination. We will mainly study organometallic compounds and silicate minerals, working both in transmission and reflection geometry. Two possible choices for Siemens D8 equipment maybe VARIO (focusing primary monochromator) and Gobel mirror systems, both of which seem rather promising. What is your experience on these systems? Did you experience other diffractometers with similar capabilities from other companies? Replies will be warmly welcome. Thanks for your attention Natale Perchiazzi § dr Natale Perchiazzi Dipartimento di Scienze della Terra Università degli Studi di Pisa Via S.Maria 53, I-56126 Pisa tel +39 050 847269 fax +39 050 500932 e-mail [EMAIL PROTECTED] §
Re: Error sum file by fullprof!!
Dear Leonardo, I use the UltraEdit-32 editor but I don't think that the problem is there. On Thu, 5 Jul 2001, Leonardo Cont wrote: Actually, under Win2000k the files can be easily opened by any text editor. Waht kind of editor or OS are you using? Regards, leonardo ___ eng. Leonardo Cont Dpt. Materials Engineering University of Trento 38050 TRENTO - ITALY Office: +39 0461 882414 E-mail: [EMAIL PROTECTED] Web: http://www.ing.unitn.it/~contl We don't need faster computers. We need better ideas. [A. Chorin, Berkeley, '00] Sono rospo...e ho detto tutto! [M. Neri, Berkeley, '00] ___
Re: Error sum file by fullprof!!
At 16:36 05/07/2001, you wrote: I use the UltraEdit-32 editor but I don't think that the problem is there. Actually UltraEdit is indeed the problem. It is an excellent editor but the doc will tell you that it will open the file as binary, not ascii if it finds what it thinks are binary characters :-) BTW people, please don't attach documents to Rietveld list mailings. Put them on a WWW server and include just a pointer to them in your email, if you can't quote the relevant part as ascii text in the body of your mail. Attachments can contain viruses, and they fill up my hard disks:-) Only exception is Bob von Dreele, who kindly posted the GSAS source for the benefit of Armel :-) Alan. Alan Hewat, ILL Grenoble, FRANCE [EMAIL PROTECTED] fax direct (33) 4.76.20.76.48 tel (33) 4.76.20.72.13 (or .26 Mme Guillermet) http://www.ill.fr/dif/AlanHewat.htm
Re: Error sum file by fullprof (and good things about UltraEdit)
UltraEdit ... will open the FullProf sum file as binary... I meant hexadecimal :-) Do cntrl-H to switch to ascii in UltraEdit. The interest of UltraEdit http://www.ultraedit.com/ is that it knows the syntax of many languages, C, Perl, Fortran etc and can be told about other syntax. It makes it easier to understand and write code. UltraEdit can even be used to edit files on your PC when the files are on a remote Unix or Vax system, with the help of another excellent application, terminal emulator NetTerm. Coupled with a little C-program NetEdit on your Unix machine http://starbase.neosoft.com/~zkrr01/ you can then graphically edit files on your Unix server from your home PC, even across a firewall on an ordinary telephone line. Amazing :-) Alan Hewat, ILL Grenoble, FRANCE [EMAIL PROTECTED] fax direct (33) 4.76.20.76.48 tel (33) 4.76.20.72.13 (or .26 Mme Guillermet) http://www.ill.fr/dif/AlanHewat.htm
Re: GSAS code
Only exception is Bob von Dreele, who kindly posted the GSAS source for the benefit of Armel :-) Unfortunately, no benefit at all until now. Still no permission for putting it in the source code museum. Bob possibly considers that his code is not old enough and may post an obsolete version some day ?-). I don't know. Anyway, I have kept it in a highly secured place ;-). Moreover, the museum entry is for free, no benefit on that side. Expected benefit for all of us would be new codes reusing parts of old ones, or new functionalities added in old codes by new programmers (for instance, some automatic stacking fault presence recognition and data analysis allowing us to get more vacations and free time while publishing no less ?-). Armel http://www.cristal.org/museum/ PS - Who said that we do not need faster computers but only new ideas ? We need both, don't we ?
