Dear Apu, your question is very clear: you have determined the space group symmetry from the systematic absences of your powder diagram and then you would like to know where are the atoms in the unit cell, isn't it? I.e. which orbits of the space group are occupied. Answering this question has been called "solving the structure" and it can be done either in extracting the intensities from the indexed pattern and then using direct methods or with temperature annealing programs... For simple structures one can also compare powder diagram and maybe you will find in a database a pattern that is matching yours.....About the number of atoms in the unit cell, difficult question..... but together with you unit cell volume it should give a reasonable density.
Regards, Marc ----- Original Message ----- From: <[EMAIL PROTECTED]> To: "Rietveld Mailing List" <[EMAIL PROTECTED]> Sent: Wednesday, November 03, 2004 4:53 PM > > Dear All, > One thing is sufferring me a lot. I don't have much idea about space groups. > In case of giving positions of atoms in GSAS, so far I understand when I am giving the space group information, I should not have to give the positions of all the atoms. It is understood from the space group information. > > For example: For fcc Nickel with space group 225, I have to only give the position of one atom (0,0,0).Not the (0.5,0.5,0.0) ... > > But I can't understand, if know the space group of a system, how can I decide what position and how many atom position I should insert in GSAS. > > I will be grateful, if anybody help me in this regard. > > Regards, > Apu > > > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ > Apu Sarkar > Research Fellow > Variable Energy Cyclotron Centre > Kolkata 700 064 > phone: 91-33-2337-1230 (extn. 3190) > Fax: 91-33-2334-6871 > INDIA > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ > > > >
