******************************************************************************* ******************************************************************************* ************************* *************************** ************************* Documentation for FIT *************************** ************************* *************************** ******************************************************************************* ******************************************************************************* PROGRAM AUTHORS : V. PETKOV and N. BAKALTCHEV, Sofia University Department of Solid State Physics, Sofia-1126, BULGARIA. REFERENCE : J. Appl. Cryst. 23 (1990) 138-140. FIT, a computer program for decomposition of powder diffraction patterns and profile analysis of pair correlation functions. USER'S GUIDE ----------------------------------------------------------------------------- ASSOCIATED DOCUMENTATION : The documentation directory "ccp14/doc/fit" contains four files - CHO - contains experimental powder diffraction data ( a test example ) CHO.IFT - contains the best values of the adjustable parameters obtained as a result of a decomposition of the CHO powder pattern using Intermediate Lorentzian analytical functions. GDCU1.PDF - contains data for the pair correlation function of Gd Cu metallic glass (V. Petkov et al. J. Non-Cryst. Sol. (1990) in press) 4 3 GDCU1.DFT - contains the best values of the adjustable parameters obtained as a result of a profile analysis of GdCU1.PDF ( a test example) ----------------------------------------------------------------------------- Getting started To start the program Input from the keyboard FIT [data file name] and press ENTER. Then: Input [parameter file name] in a response to the prompt and press ENTER. (The corresponding values of the parameter file will be assigned to the adjustable parameters and to the parameters controlling the fitting procedure.) Or press the ESC key if the program is started for the first time with new experimental data and an old parameter file is not available. In that case the user have to take care to input reasonable initial values for all of the parameters. After starting the program the menu mode is activated. Strictly follow the steps of the upper right window - i.e the menu window. Move the prompt to the desired step by means of the Arrow keys. Press ENTER to activate the selected step of the fitting procedure. A definite step can be activated only if the preceding steps have been passed successfully. Auxiliary commands in the menu mode of operation: Press - Ctrl-B to change the screen background colour (supported only by CGA/EGA graphic cards) Ctrl-Q to quit the program FIT Ctrl-T to check for the available free core memory Esc to cancel the last input/command ------------------------------------------------------------------------------- Menu Mode- Step One: Smoothing - for the theoretical background see the paper of Savitzky & Golay (1964) Anal. Chem. 36,p. 1627 Step Two: Background correction - for the automatic background correction and the meaning of the parameter Q see the paper of Sonneveld & Visser (1975) J. Appl. Cryst. 8, p.1. ( a0...a8 are the coefficients of the polynomial approximating the background) Step three: Profile Differentiation - see the paper of Savitzky & Golay The user can detect peaks by the maxima of the fourth experimental profile derivative which is displayed on the screen together with the experimental data or can activate the graphical mode of operation, substitute the fourth with the second derivative and detect the peaks by the minima of the second derivative. Step four: Profile Fitting ROIL; ROIR - the left and the right limit of the region of the diffraction pattern being fitted. G - Gaussian L - Lorentzian M - Modified Lorentzian l - Intermediate Lorentzian P - Pearson VII V - Pseudo-Voight D - Profile analysis of Pair Correlation Functions T - demonstration run without minimization S - standard least-squares minimization algorithm G - steepest descent minimization algorithm Ro - average atomic density in [at/A**3] - needed only for the profile analysis of Pair correlation functions (PCF). R(%) - weighted-pattern R factor Re(%) - expected R factor Standard parameters of the individual peaks: X0 - position Y0 - Height 2W - FWHM m - polynomial power (only for P VII) 1 < m < 999 à - L fraction in V (only for V) 0 < à < 1 C - coordination number (only for D) x - limit beyond which the structural correlations c can be neglected ( only for D ) ( For a more detailed definition of the parameters of the Pearson VII and Pseudo-Voight analytical functions see the papers of Langford (1987) Prog. Crys. Growth and Char. 14, p.185 or Young and Wiles (1982) J. Appl. Cryst. 15, p.430.) ( The theoretical background of the profile analysis of pair correlation functions is described in the papers of Hajdu (1980) Phys. Stat. Sol. A60, p.365 and Petkov, Apostolov & Skumrjev (1989) J. Non-Cryst. Sol. 110, p.184 In the present version of FIT for the sake of uniformity the parameter á has been substituted with the parameter W ) Assignment of initial values of the adjustable parameters: There are four different ways to set up the adjustable parameters : * "default" assignment. An old parameter file is needed prior to starting the program. * "by hand" assignment. All of the parameters are inputted by hand in a res- ponse to the corresponding prompts. The necessary values are taken from the current coordinates of the cursor ( the lowest right window ). For example - the cursor is is positioned over the peak under consideration and its "xi" and "IN" coordinates are inputted by hand as x0 and y0 peak coordinates. * "semi-automatic" assignment. Firstly the cursor is positioned over the considered peak. Than by simultaneously pressing the Ctrl-Enter keys its coordinates are read out and on this basis a rough estimation for the peak parameters is computed. By pressing the Enter key these estimations are confirmed and assigned as initial values of the adjustable parameters. * "automatic assignment". An option is added which allows automatic peak location and automatic assignment of initial values of the adjustable parameters of the located peaks. This way of assignment is recommendable in the first stages of the pattern decomposition and only in the case of powder pattern decomposition. It is also recommendable to fit a powder pattern with relatively simple G;L;I; or M analytical functions at first and then to use the adjustable parameters obtained as initial values in a fitting with the more complex P and V functions. To cancel the last input/command press the ESC key. Pressing the ESC key two times will result in quitting the step four. To interrupt the fitting process Press Ctrl-I keys. Special case of profile analysis of PCF: In case good estimates for the initial values of the coordination numbers C are not available one can press ESC key and input the corresponding peak height instead. On its base a reasonable estimate for C is computed and used in the profile fitting. The parameter ROIR is overwritten by the parameter x . c Step five: Save Fit - creates a parameter XXXXXX.?ft file, where ? stands for one of the letters from L to D. This file contains the parameters which control the fitting procedure, the R factors and the parameters of the individual peaks x0 - position; y0- height; A - area; 2W - FWHM; 2Wi - integral breadth; C - coordination number ( only for D ). Step six: X-Y Data File - creates a XXXXXX.plt file which contains experimental data (1); corrected exp. data (2); Background (3); First (4), Second (5) or fourth derivative (6); fitted data (7); residual difference (8); individual peaks (9) or all these data together depending on the user's choice. Step seven: New data - allows restarting with new data without quitting the program FIT. -------------------------------------------------------------------------------- Graphical mode of operation: To activate the graphical mode of operation move the prompt to the left window using the Arrow keys and press Enter. Press - Ins/Del Keys to re-scale the graphics - F1 to F10 and Ctrl-Fi (i=1-10) to change the graphics - the Arrow and Ctrl-Arrow Keys to move the cursor fast and slow - PgUp/PgDn keys to see the individual peaks - Ctrl-H - to see the built-in help To exit from the graphical mode press the ESC key. -------------------------------------------------------------------------------- DEMONSTRATION: Use the data file CHO and the parameter file CHO.iFT as a demonstration run for powder pattern decomposition. Use the data file GDCU1.PDF and the parameter file GDCU1.DFT as a demonstration run for profile analysis of PCF. It is instructive at first to confirm all of the parameters which control the fitting procedure (simply by pressing the ENTER key) in order to get an impression how do the program works and then to change some of the parameters on your choice. -------------------------------------------------------------------------------- File format: The raw data file is a text file which contains two columns of numbers in free format ( x and y coordinates of the considered profile ) separated by blank. The XXXXXX.plt file contains from two to ten columns of numbers (depending on the user's choice) separated by blanks. The XXXXXX.?ft parameter file has a special architecture which should not be changed if it is to be used for another run of the program FIT. ------------------------------------------------------------------------------- We hope that the program FIT will be useful in your research work. With best regards - V. Petkov and N. Bakaltchev. -------------------------------------------------------------------------------