Limitations

The ARP/wARP procedure requires the use of reciprocal space refinement, density map calculation and the ARP/wARP software itself. The minimisation can be done with the CCP4 [9] program REFMAC [11]. Use of other programs for minimisation, e.g. SHELXL [12], requires additional conversion to the CCP4 format which is provided within the ARP/wARP package. Density map calculations are carried out with the CCP4 programs FFT and MAPMASK.
As ARP/wARP runs in conjunction with programs of the CCP4 suite all limitations of the latter remain. Note that the CCP4 ARP version, arp_waters, is not equivalent and is not compatible with the full ARP/wARP package. ARP/wARP itself is limited to:

1. The CCP4 conventions should be set up before running ARP/wARP 
2. Density maps and reflection MTZ files in the CCP4 format
3. ARP/wARP operates with coordinate files in standard PDB format
4. Only acentric space groups (typical for proteins) and P1 are supported