TITLE A title of up to 78 Characters

CELL The wavelength (ignored at present) followed by the unit cell parameters A, B, C, alpha, beta, gamma. The 2D code only uses A,B and gamma.

SYMM The 2D symmetry, e.g. p2, p6mm. All the 2D groups (plus the alternates with the axes switched) are recognized.

SFAC The atoms to use, a list of 1-4 characters (including ions if the scattering factors are known)

UNIT The number of atoms of each type in the SFAC command, in the same order.

TFAC Temperature Factors (B). If these are not given, they default to 0.6. While methods exist for fitting these with 3D data, they do not work for 2D data. (The exact value is not that important.)

AOCC Occupancies for each type. If this is not included, occupancies of 1 are assumed

ELECTRON Tells the program to convert the x-ray scattering factors using the Mott formula

CHANGE Tells the program to consider all reflections are freely variable. If this is omitted then all non-zero phases specified in the name.hkl file are considered to be fixed (to specify a fixed phase of 0 degrees, use 360).

ORIGIN Tells div2D to find the origin for you

4.2 Display Parameters (peaks2D and fs2D)

TIMES Scaling (magnification) of images, defaults to 1.

WIDTH Number of unit cells across in the images, defaults to 1

HEIGHT Number of unit cells down in the images, defaults to 1

SEMPER Will produce an image that can be read by Semper

ATOMS n1 This will constrain the solution to have at least n1 peaks in it. This is a powerful constraint that can help with larger structures, although case should be taken to underestimate the value of n1.

This is the most complicated part of the program. If you are unclear, it is best to leave these alone at the default values. If unclear and you also want to be conservative only include the command MODE ENTROPY.

MODE This controls the precise algorithm used in the projection onto sets.  

Entropy Use only the relative entropy (similar to a Maximum Entropy approach - for more see Ref. [5])

Mixed 2/3 Entropy and 1/3 Positivity (Default)

Equal 1/2 Entropy and 1/2 Positivity

Positive Uses Positivity only. This is not recommended unless you already know a large number of the phases

PLAM num The over-relaxation value for positivity (Default=1.25) is determined by the value of num. This should be in the range 1-2

LAMB n1 n2 The over-relaxation value for the phases (Default=1.5) is given by n1. The value of n2 determines the speed of turn-on of the over-relaxation in one of two ways. If a numerical value is given, then the over-relaxation lambda is:

lambda = 1 + (n1-1)*[1-exp(-n/n2)]

where n is the iteration number, starting at zero. Values of 1-3 are reasonable for n2. As an alternative (Default) the program will do an automatic adjustment if AUTO is specified.

NORM OFF Tells the program not to normalize the data. Warning: the code will assume that you have given it properly scaled U(k) values such that U(0)=1.

WIND OFF Tells the program not to use a window to reduce ringing in real space - not a good idea.