LCHK - LAUE DATA COLLECTION STRATEGY ==================================== INTRODUCTION This program analyses the distribution of symmetry-unique reflections in a Laue pattern. LCHK is intended to complement the program NEWLAUE, and most of the conventions assumed in NEWLAUE are followed in LCHK. Please note that LCHK always deals with UNIQUE reflections. The program was originally written by M.Elder and has been revised by I.J. Clifton and J.W. Campbell subsequently (Daresbury Laboratory). When the program starts the option menu is displayed on the left. Options may be selected by typing the first four characters. The current default option is displayed in square brackets. CTRL/Z reprints the option menu. This may be necessary on some terminals if the alpha screen is erased after a plot has been displayed. CTRL/Z may also be used to cancel any other prompts throughout the program (but not cancel cursor options). List of sections: Parameters Analysis Commands Other Commands PARAMETERS Introduction This section describes the parameters used by the LCHK program. List of subsections in this section: CELL WMIN WMAX DMIN DISTANCE RADIUS SPDR BMDR PX PY PZ SYSTEM LATT SPINDLE SCALE CELL The CELL parameters, A*, B*, C*, ALPHA*, BETA* and GAMMA* are used to determine the shape of the reciprocal unit cell. Not all these parameters are needed in more symmetric crystal systems (see SYSTEM). Each parameter is individually selected by name and the program prompts for input value (cell length in Angstroms**-1, angles in degrees). Note that the cell lengths are subject to the effects of the SCALE parameter (q.v.) For some crystal systems only some of the parameters need be defined, e.g., for Cubic systems only A* is sufficient, B*=A*, C*=A*, ALPHA=90, BETA=ALPHA, GAMMA=ALPHA are implied. If the user insists in supplying values to surplus parameters, correct or incorrect ones, the program will ignore them, in fact it resets them when the calculation starts. In such cases the list in the Menu and the hard copy will leave the value field blank. WMIN The minimum wavelength value in Angstroms. WMAX The maximum wavelength value in Angstroms. DMIN This sets the lower limit on the interplanar separations included. To consider all spots choose DMIN < WMIN/2. High order index planes (and hence in general weak reflections) will have small interplanar spacings. The value of DMIN cuts off the spots due to interplanar spacings smaller than that length (in Angstroms). DISTANCE Sets crystal to film distance (in mm). RADIUS Prompts for radius of the exposed area of the film (in mm). Topographers Note: The cassette used in topography stations is square with half-diagonal (equivalent to radius here) of 50mm. SPDR Prompts for reciprocal axis along rotation axis BMDR Prompts for reciprocal axis nearest x-ray beam axis in plane defined by beam axis and rotation axis. PX Prompts for rotation angle phi_x (Deg) about the axis X along the beam axis. NEWLAUE assumes that the beam is normal to the film. Positive is clockwise, looking in the same direction as the axis. PY Prompts for rotation angle phi_y (Deg.) about axis Y perpendicular both to the beam and the spindle axis, forming a right-handed set with these axes. The Y axis corresponds to the x (horizontal) axis of the coordinate system of the film. Positive is clockwise, looking in the same direction as the axis. PZ Prompts for rotation angle phi_z (Deg.) about axis Z along the spindle axis. This axis corresponds to the y (vertical) axis of the coordinate system of the film. Positive is clockwise, looking in the same direction as the axis. SYSTEM Together with the centring 'LATT' parameter sets the crystal system and type. Choices for SYSTEM are: Triclinic Monoclinic Orthorhombic Tetragonal Hexagonal (includes rhombohedral on hexagonal axes) Rhombohedral (rhombohedral axes) Cubic LATT Sets the centring type of the lattice. Choices are: A, B, C One-face centred F All-face centred I Body centred R Rhombohedral centring (SYSTEM=hexagonal only) SPINDLE Defines the value of Spindle angle setting (in Deg). It is used on the oscillation/Laue camera to rotate the crystal. The spindle axis is always assumed to be perpendicular to the beam. It defines the Z axis and hence the Y axis (see PY, PZ). Clockwise is positive. SCALE This is a scaling factor which applies to the reciprocal cell lengths. It can be used to speed up the calculations by making LCHK consider a unit cell which is some fraction of the real one. The results of LCHK should not change much as SCALE is altered, but some care may be needed interpreting the results when SCALE is not 1. ANALYSIS COMMANDS Introduction The commands described in this section all vary one or more parameters and produce tables of those parameters against the number of uniques recorded. List of subsections in this section: ROTATE SEARCH WAVVAR VARCF RESOLN ROTATE This command has unfortunately not been documented. SEARCH This varies PZ (along the spindle) and PY independently and produces a matrix of the number of uniques at each step. NB The current value of SPINDLE is ignored in this option --- the values of PZ are therefore `absolute'. WAVVAR This command is concerned with those unique reflections which have symmetry equivalents (`duplicates') recorded on the same film, and the wavelength differences within these sets of spots. The program first calculates the number of such sets of reflections and the total number of such reflections. For each set of a unique and its duplicates, it calculates an average wavelength, and accumulates the average deviation of the set from that average. It then prints out a histogram of the deviations. VARCF Increases the crystal-film distance in steps starting from its current value. RESOLN This command partitions the uniques into resolution bins (running from DMIN to the lowest resolution found (dmax)). A table of cumulative fractions of the uniques is produced, running from dmin to dmax and vice versa. OTHER COMMANDS Introduction Thsi section describes the other commands avaialble within the program LCHK. List of subsections in this section: DATGET DATSAV HELP STOP DATGET The DATGET command allows the user to retrieve data created by a previous run of the program or in user edited file. The extension ".dat" is automatically added to the file name. **** ONLY FILES IN CURRENT DIRECTORY ARE ACCEPTED. **** A badly formatted file is likely to result in the program crashing. DATSAV The DATSAV command allows the user to save the data currently in use concerning the experimental set-up in a file. It can be retrieved using DATGET (q.v.) **** The extension, ".dat" is always added to the file name. *** **** ONLY FILES IN CURRENT DIRECTORY ARE ACCEPTED *** HELP The HELP command has now been withdrawn as its impementation was Vax specific. The information that was presented is now available in this documentation file. STOP Ends the program and resets the screen. If you abort the program by using the CTRL/C or CTRL/Y keys you will need to reset the terminal manually with the SETUP, RESET keys.