Crystallography Laboratory University of Nijmegen

7. Solving a structure of your own

Open the directory where you would like to solve your structure. In the following 'code' stands for the name of your compound. This may be any suitable abbreviation, of course. If you already have a file in there named 'code.crysin' so much the better. If not, Crunch will prompt you for the information required. The file code.crysin will be created.

The file code.crysin contains the usual crystallographic data such as cell constants, wavelength used, cell contents etc. It is important to give the cell contents as accurately as is possible. Next, you need a file containing h,k,l, F and sig(F), one reflection for each record, with proper separation between numbers (spaces, comma's or a plus or minus sign are required).

The values for h,k,l should be consecutive on your file. However, the other variables may occur in any order. E.g. the hkl may be the last three numbers etc. In the record other numbers may be present, the program will skip them if required. Before you do anything else this file must be converted into a 'code.frefa' file. Type

crunch code conhkl "filename" 

crunch code try 1 5

Use the defaults indicated. Crunch determines automatically whether to treat the problem as a heavy atom structure or an equal atom one. In some cases you are given the option to treat for instance an organic compound containing chlorine as an equal atom problem. Basically you just give return a few times, Crunch will use sensible defaults and your structure will be solved. Try larger values of the last number given - 5 in this case - if you expect the solution to be difficult. Your structure should come out if all goes well. Crunch is a multi solution method. In the example given, 5 random starts will be used to find the solution.

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