Feature and organization

The package of computer programs was designed to meet five specific objectives which will be briefly discussed below.

1. It should be possible to replace existing functions or add new functions without modifying existing code.
2. The programs should have a common mechanism for reading data.
3. It should be easy to define standard geometry for new and unusual chemical groups.
4. Is should be possible to constrain specified groups of atoms to behave as rigid bodies or to be held constant during refinement.
5. The program should provide tools to aid the user in the detection of errors in the model that are beyond the ability of the refinement package to correct.

Because of the ability to replace easily the programs performing specific calculations, the most efficient algorithms for a particular problem can be used. This feature has resulted in a package with great flexibility and speed.

• Overall organization
• Data input and data transfer
• Geometry definition
• Rigid-body refinement
• Detection of errors in the model