Parameters to consider setting if SOLVE does not find a satisfactory solution

If SOLVE does not find a good solution atomatically, there are a few parameters that you might consider setting to tell it how to go about its search. Some of these are:

• THOROUGH. This keyword tells SOLVE to keep looking through all the seeds even if a good solution (figure of merit greater than 0.5, score greater than 10) has been seen. The default is QUICK, the opposite of THOROUGH.
• RATMIN. This keyword specifies the minimum F/sigma that will be used. The default is 2.0. SOLVE may be tossing too much of your data if it is weak.
• RESOLUTION. This keyword tells SOLVE the resolution limits to use. If they include high resolution but the data is very poor there, this could prevent SOLVE from finding a solution at high resolution.
• RESOLUTION_STEPS. This keyword (default = 1) tells SOLVE to cycle through shells of resolution. Sometimes SOLVE can find a solution at low resolution but not high resolution or vice-versa. Try a value of 3 if 1 does not work.
• CUTOFF_DERIV. This keyword can be used to give SOLVE more restrictive resolution limits for a particular derivative, wavelength, or native dataset than the overall resolution limits specified with RESOLUTION.
• FP_OR_FM. This keyword tells SOLVE to keep reflections in MAD datasets where only F+ or only F- have been measured. If MAD data are very incomplete, SOLVE may be tossing too much data in its effort to only use matched F+/F- pairs. The default is FPFM_ONLY, only use matched pairs.
• FIXSCATTFACTORS vs REFSCATTFACTORS. These keywords tell SOLVE whether to fix or refine scattering factors f' and f". If your MAD data is pretty weak, refining scattering factors can lead to worse estimates than you started with.
• NANOMALOUS and NRES. These define the number of anomalously scattering atoms and protein residue equivalents in the asymmetric unit. NRES defines the overall scale of the data. The ratio of NANOMALOUS to NRES defines how big the expected scattering contribution from the anomalously scattering atoms should be. Additionally NANOMALOUS defines the maximum number of sites for the anomalously-scattering atoms (unless the keyword NSOLSITE is set, in which case the NSOLSITE value is used).
• NSOLSITE and NSOLSITE_DERIV. These keywords define the maximum number of heavy atom sites either for the dataset as a whole (NSOLSITE) or for a particular derivative (NSOLSITE_DERIV). You can use them to control how much time SOLVE will spend in various derivatives.
• INANO. This keyword tells SOLVE to use anomalous differences for a derivative. If you leave it off it will not include them for MIR data. (For MAD data SOLVE will include anomalous differences unless you tell it not to with noinano).
• NOANOREFINE. This keyword tells SOLVE that even if INANO is specified for a particular derivative, the anomalous differences will not be used in heavy atom refinement. This is the default for MIR data and should be used for MIR or MAD data if the anomalous data are much weaker than isomorphous differences.
• ACCEPTANCE. This keyword tells solve how weak a site can be but still get accepted. Sites that have occupancies of about ACCEPTANCE times the average for other sites are typically accepted (but this is not a simple cutoff, it is a parameter in the overall scoring procedure). If you are not getting as many sites as you would like, try lowering the value of ACCEPTANCE (default =0.2).
• NSEEDSOLVE. This keyword tells solve how many seeds to try (default=5). If SOLVE isn't finding anything, you could try more.
• NTOPSOLVE. This keyword tells SOLVE how many solutions to keep track of at any one time. If SOLVE isn't finding anything, you could increase it (default=5). Note that this will slow things down a lot if you increase it by much.
• ICRMAX. This keyword tells solve how many peaks in the Patterson function to try as potential cross-vectors in a 2-site search. Try increasing it from 30 to a higher number.