Keywords in
Structure-Model Files

Structure-model files are formatted text files with the extension MOD. They consist of a number of sections begining with a comment line and ended with the *EOS (end of section) line. In between these two lines, there are command lines begining with a space followed by a keyword and parameters.

Section
 Keyword 
Command in Fortran Format
Private
CONV
( 1X , 'CONV' , 4X , I4 ) n
 n = 1: conventional structure model
 n = 0: incommensurate modulated structure model
TYPE
( 1X , 'TYPE' , 4X , I4 ) n
 n = 0: projected model along the [100] direction
 n = 1: projected model along the [010] direction
 n = 2: projected model along the [001] direction
 n = -1: 3-dimensional model
XRAY
( 1X , 'XRAY' , 4X , I4 ) n
 n = 0: electron diffraction will be simulated
 n = 1: X-ray diffraction will be simulated
 Omitting this command is equivalent to set n = 0.
RECI
( 1X , 'RECI' , 4X , 5F8.2 ) Ax , Ay , Bx , By , Zoom
( 1X , 'RECI' , 4X , 7F8.2 ) Ax , Ay , Bx , By , Qx , Qy , Zoom
The first command is for conventional structures, while the second is for incommensurate structures. These commands are used to inform VEC how to display the 2- or 3-dimensional diffraction pattern in a window.
 X and Y are respectively the horizontal and vertical axes of the window with the origin at the upper-left conner.
 A and B are vectors representing two of the three axes a, b and c, which define the crystallographic unit cell.
        For [100] projections, A = c , B = b.
        For [010] projections, A = a , B = c .
        For [001] projections, A = a, B = b.
 Ax, Ay: X, Y components (in pixels) of the vector A
 Bx, By: X, Y components (in pixels) of the vector B
 Qx, Qy: X, Y components (in pixels) of the modulation vector q
 Zoom: linear scale factor of the displayed model
SIZE
( 1X , 'SIZE' , 4X , 4I8 ) Ox , Oy , W , H
Ox, Oy: X, Y coordinates (in pixels) of the unit-cell origin in the model window
W, H: width and height (in pixels) of the model window
                        ------------------------------------
Omitting commands SIZE and RECI does not affect subsequent operations on the model window. However, in this case the model image will not display properly.
 Cell
CELL
( 1X , 'CELL' , 5X , 6F10.4 ) a , b , c , a , b , g
This defines the crystallographic unit cell with a , b and c in Angstroms and a , b and g in degrees.
QVEC
( 1X , 'QVEC' , 5X , 3F10.4 ) k1 , k2 , k3
This defines the modulation wave vector q = k1a* + k2b* +  k3c*
Symmetry
SGSY
( 1X , 'SGSY' , 5X , 2I4 ) n , i
 n: symmetry order of the space group - the maximum nember of independent symmetry operations
 i = 0: noncentrosymmetric
 i = 1: centrosymmetric
SYOP
( 1X , 'SYOP' , 5X , 3 ( 3I2 , F10.7 , 4X ) ) ( ( R ( I , J ) ,  J = 1 , 3 ) ,  T ( I ) ) ,  I = 1 , 3
( 1X , 'SYOP' , 5X , 4 ( 4I2 , F10.7 , 2X ) ) ( ( R ( I , J ) ,  J = 1 , 4 ) ,  T ( I ) ) ,  I = 1 , 4
The first command is for conventional structres while the second is for incommensurate modulated structures.
Each command (a single line) defines one symmetry operation, which consists of a rotation R ( I , J ) and the associated translation T ( I ). There will be n SYOP lines for a space group of the order n.
ATOM
ATCO
( 1X , 'ATCO' , 4X , A2 , A6 , 6F8.5 ) symbol , code , x , y ,z , B-factor , occupancy , valence
This defines the species (atomic symbol), identify code, positiion (in fractional coordinates), isotropic temperature factor B = 8p2U and valence of an atom. 'valence' is temporarily void.
UIJ
( 1X , 'UIJ' , 4X , A2 , A6 , 6F8.5 ) symbol , code , U11 , U22 , U33 , U12 , U23 , U13
This defines coefficients of the anisotropic temperature factor of the given atom defined by the preceding ATCO command.
XWAV
( 1X , 'XWAV' , 4X , A2 , A6 , 9F8.5 ) symbol, code, C0 , C1 , C2 , C3 , C4 , S1 , S2 , S3 , S4
This defines the X component of the positional modulation of the given atom.
 Cn: the nth order coefficient for COS functions in the Fourier-series expansion*
 Snthe nth order coefficient for SIN functions in the Fourier-series expansion*
YWAV
( 1X , 'YWAV' , 4X , A2 , A6 , 9F8.5 ) symbol , code , C0 , C1 , C2 , C3 , C4 , S1 , S2 , S3 , S4
This defines the Y component of the positional modulation of the given atom.
 Cn: the nth order coefficient for COS functions in the Fourier-series expansion*
 Snthe nth order coefficient for SIN functions in the Fourier-series expansion*
ZWAV
( 1X , 'ZWAV' , 4X , A2 , A6 , 9F8.5 ) symbol , code , C0 , C1 , C2 , C3 , C4 , S1 , S2 , S3 , S4
This defines the Z component of the positional modulation of the given atom.
 Cn: the nth order coefficient for COS functions in the Fourier-series expansion*
 Snthe nth order coefficient for SIN functions in the Fourier-series expansion*
PWAV
( 1X , 'PWAV' , 4X , A2 , A6 , 9F8.5 ) symbol , code , C0 , C1 , C2 , C3 , C4 , S1 , S2 , S3 , S4
This defines the occupational modulation of the given atom.
 Cn: the nth order coefficient for COS functions in the Fourier-series expansion*
 Snthe nth order coefficient for SIN functions in the Fourier-series expansion*

* For detailed description of a modulated atom, see the relevant theory.