First additional line
FIRST PART : For each case is given the formula (or name), space group, total number of independent atoms (C1), number of refined x,y,z parameters (Nc), number of independent atoms (C2) obtained from application of direct or Patterson methods (the starting model allowing then completion of the structure determination by Fourier syntheses). In some cases, the structure was determined by molecular modelling techniques (MM) or model bulding (MB). In such cases C2 is replaced by C3 which is the number of independent molecules of which the positions are searched in the cell for corresponding to an optimum by Monte Carlo, Patterson-search, Genetic Algorithm (...) methods. Sometimes the structure was guessed (C2=G) or a partial model was deduced by analogy with a known structure (C2=A). C1, Nc, C2 and C3 give an idea of the structure complexity and of the level of difficulty encountered to obtain the initial model. The high cell volume is not an indice of complexity, unless it is moderated by the crystal symmetry : 2000 Angstroem-cube is difficult with P1 (with nearly 100 independent atoms to find), easy with Fd-3c (nearly 0.5 atom to find if all in general position), however the problem of reflections strictly overlapping is important in the latter case... Finally, the data type used for the determination is given : Sync=synchrotron X-rays; XC1=conventional X-rays monochromatic (K-alpha 1) ; XC12= conventional X-rays (K-alpha 1+2) ; N=neutrons.
SECOND PART after / : Six informations concerning programs and/or methods used are mentioned (there are some exceptions), separated by commas. These informations are related to six important operations generally performed successively in order to complete a structure determination from powder diffraction data. In fact, a supplementary one is not given which would have rank 0 chronologically: the extraction of the angular reflection positions before indexation. Explanations on the six operations follow (to obtain references for the cited programs, look inside the papers citing them) :
Example of reference with the first additional lines :
- Determination of complex structures from powder diffraction data: the crystal structure of La3Ti5Al15O37, R.E. Morris, J.J. Owen, J.K. Stalick & A.K. Cheetham, J. Solid State Chem. 111 (1994) 52-57.
La3Ti5Al15O37, Cc, C1=60, Nc=178, C2=5, Sync+N / ?, GSAS, EQUI, MULTAN84 (DM), GSAS, GSAS the six informations mentioned above : / 1, 2, 3, 4, 5, 6Second additional line
Example of reference having the second additional line :
48)- Structure determination of NiV2O6 from X-ray powder diffraction
: a rutile-ramsdellite intergrowth, A. Le Bail & M.-A. Lafontaine,
Eur. J. Solid State Inorg. Chem. 27 (1990) 671-680.
NiV2O6, P-1, C1=15, Nc=42, C2=9, XC12 / TREOR, ARITB, EQUI, SHELX-76 (DM), SHELX-76+ARIT4, ARIT4
C- Ein neuer strukturtyp der oxovanadate MV2O6 : NiV2O6, Hk. Muller-Buschbaum und M. Kobel, Z. Anorg. Allg. Chem. 596 (1991) 23.
You may want to know more about C1 and C2.
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Armel Le Bail