SOLOMON (CCP4: Supported Program)


solomon - density modification (phase improvement) by solvent flipping.


solomon MAPIN [ MAPOUT ] [ RMSMAP ]
[Keyworded input]


Solomon is a program which modifies the electron density maps by averaging, solvent flipping and protein truncation [1]. It can also remove overlapped parts of a mask between itself and its symmetry equivalents. Please note that this program has various non CCP4 standard features.


Several stages are required for phase refinement with Solomon. The stages described here assume that the phase probability distributions were determined experimentally (i.e. SIR, MIR, MAD).

  1. Determine phase probability distributions, described by Hendrickson-Lattman coefficients. This is done automatically by MLPHARE.
  2. Calculate the map to be flattened. Initially, you will have a map calculated from experimental phases. It is advised that you start from a resolution which has got significant phase information and do not yet extend the resolution!
  3. Subsequent maps can be calculated from coefficients produced by SIGMAA. This gives the advantage that missing reflections can be estimated from the corresponding Fc (calculated from the flattened map). The procedure can be improved by substituting in this way for the low resolution reflections that are missing.

  4. Have a look at the map and compare it with the original FOM weighted map. If there is no non-crystallographic symmetry, you might get some additional improvement by playing around with the solvent multiplication factor and the truncation level (see the keywords TRUNC and MULSOLV). If the crystals contain a lot of solvent (70 to 80%) you might try phase extension, but make sure the map actually improves by doing so. If you have got very weak phase information at higher resolution, try including it from the start, but keep the RADIUS at the lower resolution. (If you have got reasonable phase information to 3.7 Å, and very weak information to 3.2 Å, use a radius of 3.7 Å, and a high resolution cutoff of 3.2 Å; don't extend to 3.2, but use all information from the first cycle).
  5. Identify and refine non-crystallographic symmetry if present. The Uppsala programmes "O", "mama" and "imp" are ideally suited for this purpose. You must remove overlap between symmetry related masks. The mask can be either in "O" or "CCP4" format.
  6. The mask will encompass a monomer. Each mask has a set of associated symmetry operators which describe how the density within this mask is related to other density within the asymmetric unit. This is a bit different from the way things are done in the "rave" package and has some advantages.
  7. Include the non-crystallographic restraints in "Solomon" and run the script again. You might need to reduce the level of truncation a bit and the solvent multiplier should probably be a bit less negative.



The input map must cover the asymmetric unit exactly. The input map (CCP4 format) is associated with the logical name MAPIN.
Input masks can either be in CCP4 or "O" style formats. The program can automatically determine which type of format it is. These masks are not associated with logical names but are input via the keyword MSKIN; this is not a standard CCP4 procedure.
Another possible input file is governed by the keyword CSYM.


MAPOUT and RMSMAP are both output maps and are in CCP4 format. They are not output by default, so if output is required this must be indicated by the keywords MAPOUT and RMSMAP.
Other output files are governed by the keywords SLVMASK and ASMASK. All output masks will be in CCP4 format.

Conversion between formats can be done with MAMA2CCP4, XDLMAPMAN or MAPMAN.

Note on SOLOMON masks

There are two ``features'' of SOLOMON masks which users should be aware of:

  1. Although SOLOMON uses the standard CCP4 map format for its input and output masks, it does not use the same convention as other programs e.g. 'dm'. In SOLOMON, mask grid points are set to 0.0 for protein and 1.0 for solvent. If you intend to import/export maps from or to other CCP4 programs then use MAPMASK to change the mask convention.
  2. Masks output by SOLOMON may suffer from artificial features, namely lines of set grid points along the mask edges away from the origin. For the time being this can be fixed by giving SOLOMON a map covering the whole unit cell plus the edges, and then extracting the whole unit cell afterwards (thus discarding the problematic sections).
    E.g. run MAPMASK before and after SOLOMON, using the XYZLIM keyword the first time to extend the mask by an extra grid point, and the second to restore the limits to the original values.


Keywords can be upper or lower case and only the first four letters are significant. Solomon echoes keywords as it reads them, allowing you to check the input. Keywords are only recognised if they occur at the start of a line, but they can be preceded by spaces or tabs. Keywords which are not found in the input are flagged to say that defaults will be used, misspelt keywords are ignored but not flagged. After reading the keyword and its specifier(s), the rest of the line is treated as a comment and ignored. Lines which do not start with a keyword are treated as comments too. In most cases, the order of the keywords is irrelevant, and you will probably find that Solomon does not read them in the order you specified anyway. However, there are a few exceptions (see MSKIN)!

Available keywords are:



(default: not verbose)
This option produces more information in the log file.


(default: no mapout)
This keyword only has a meaning when Solomon is modifying the electron density. The modified map will be written to the file associated with the logical name MAPOUT.

SLVFRC <value>

(default: 0)
Defines the fraction of the map to be treated as solvent. The protein mask is assumed to be a connected volume without small islands. Sometimes (especially during the first cycles) a larger fraction of the map than actually specified will be treated as solvent. This is because small islands with a high local standard variation (i.e. look like a protein region) are included in the solvent region.

RADIUS <value>

(default: 3.5)
The solvent region is determined from the local standard deviation of the map within a sphere of a radius specified in Angstroms. The standard deviation is calculated relative to the mean solvent density, which by default is assumed to be the same as the whole map, but which can be changed with the keyword SLVDENS. Solomon also produces a histogram of the local standard deviation allowing you to make a judgement of the separation between solvent and protein. This histogram is printed if you specify VERBOSE. The mask can be inspected with the RMSMAP or the SLVMASK commands. Tests suggest that the optimum size of the radius is about the resolution limit to which significant phase information is available. Do not set it too high! The algorithm for determining the solvent mask is different from the Wang-algorithm, which needs larger radii!


(default: not output)
A map containing the local standard deviation at each grid point is written out (associated logical name is RMSMAP). This map can be manipulated with CCP4 programs and inspected within "O". Solomon will inform you about the appropriate contour level to choose to see the solvent boundary.

SLVMASK <filename>

After determining the solvent mask, it will be written to disk as specified. See INPUT AND OUTPUT section for information on mask format.

SLVDENS <value>

(default: 0)
The mean density of the solvent after subtracting the F000 term. The solvent mask is determined from the local standard deviation from the mean density of the solvent, which by default is assumed to be the same as the whole map. However, inclusion of (possibly reconstructed) very low resolution terms can change the mean solvent density significantly. This keyword allows one to correct for this.

MULSOLV [AUTO] <value>

(default: -1.00 with AUTO or -0.75 without)
Defines the multiplier used to modify the solvent density with respect to its mean, the flipping factor. For conventional solvent flattening, set this value to 0. For solvent flipping, set this value to -1. Tests on crystals with a solvent content of around 50% suggest that there is a clear relationship between the optimal flipping factor and the level of truncation. Therefore it is advisable to use the "AUTO" option, which scales the solvent multiplier by the ratio between the variance of the protein after and before truncation.

Tests also indicate that when the solvent content is higher than 50%, the solvent multiplier needs to be made less negative than with lower solvent content. In a test case with significant data to 3 Å and a solvent content of 33%, the best results were obtained with "MULSOLV AUTO -1.6".

TRUNC <minvalue> <maxvalue>

(default: 0.35 1)
Defines truncation levels.

        trunc 0.05 0.95

will truncate the lowest and highest 5 percent of the protein area of the map. Tests strongly suggest that by truncating the lower 30 to 40% of the protein, major improvements of the phases can be obtained. It is likely that there is a relationship between the optimum level of truncation and the maximum resolution of the data. In test cases of crystals diffraction beyond 3 Å, the optimum lies between 30 and 40%.

PTOS <value>

(default: 1.31)
Ratio between the mean protein density and the mean solvent density. This is used in conjunction with EXTRUDE.


(default: not extrude)
By specifying "EXTRUDE", very low resolution structure factors will be reconstructed. If low resolution terms are missing or are not well phased, the mean protein density will be almost equal to the mean solvent density. If the density modification procedure is used to also reconstruct missing terms (by using the program SIGMAA or FFT to substitute Fc), a constant value (which can be negative) will be added to the grid points in the solvent, adjusting the mean ratio between protein and solvent to be as given by PTOS. It is assumed that the lowest density found within the protein region is zero after adding in an F000 term. The main function of this keyword is to prevent the inflation of the mean protein density during iterative density modification caused by truncating protein density on every cycle.

CSYM <filename>

(default: operators from mapfile)
"O"-style crystallographic symmetry operators. If this keyword is omitted, the symmetry operators from the input map are used.

ASMASK <filename>

(default: none)
This keyword only has a meaning when Solomon is removing overlap and generating new masks. If this keyword is given, a mask will be written to disk which defines the area of the asymmetric unit covered by all the other specified masks. See INPUT AND OUTPUT section for information on mask format.

MSKIN <filename>
TRANS <filename>
[MSKOUT <filename>]

A "mskin" keyword, defining the filename of an "O"-style mask or a CCP4 style mask. The "O" masks are similar in format and are ASCII files. This keyword is followed by the transformations of the mask producing the symmetry related copies ("trans" keyword). The transformation matrices are read from an ASCII file (see example below) and are in the 'O' style. However, Solomon can read these files with or without the normal 'O' data block header. Like in 'dm' the translation part is in Angstrom units. Do not forget to provide the unit symmetry operator too!!

If a "trans" keyword is followed by the "mskout" keyword, averaging will not be undertaken, but instead the masks will be checked for overlap, and where overlap occurs, this will be removed by dividing the common volume between the overlapping masks. The trimmed masks will be written to disk as specified by the filename following the "mskout" keyword. CCP4 masks will not need to be trimmed if generated from MAPMASK or NCSMASK. The output mask will have the same format as the input mask.

An example:

        mskin r1.msk
        trans unit.ncs
        mskout r1trim.msk
        trans r1tor3.msk
        mskout r3trim.msk

No averaging will be undertaken (at least one "mskout" keyword was present in the command file).

Any overlap between the mask and any of its symmetry related copies (either crystallographic, non-crystallographic, or a combination of both) will be removed, and the resulting symmetry related masks will be written to disk with the specified filenames.

In addition, "O"-style non-crystallographic symmetry operators will be written to disk. Their filenames are constructed by replacing the extension of the new mask by "ncs%d", where "%d" is an integer, indicating which symmetry is described. The integer indicates the mask which will be generated by the symmetry operation:

        r1trim.ncs0 : unity operator
        r1trim.ncs1 : generates r3trim.msk from r1trim.msk
        r3trim.ncs0 : generates r1trim.msk from r3trim.msk
        r3trim.ncs1 : unity operator

Another example:

        mskin r1trim.msk
        trans r1trim.ncs0
        trans r1trim.ncs1
        mskin r3trim.msk
        trans r3trim.ncs0
        trans r3trim.ncs1

The density in "r1trim.msk" will be averaged with the density as defined by the symmetry operators "r1trim.ncs0" and "r1trim.ncs1". Likewise, the density within "r3trim.msk" will be averaged. The maps produced by averaging contain just the density local to the specified maps, and are on the same scale. Their filenames are constructed by replacing the extension ".msk" by ".map". So, the files "" and "" are produced.


  1. Abrahams J. P. and Leslie A. G. W., Acta Cryst. D52, 30-42 (1996)


Jan-Pieter Abrahams, MRC Laboratory of Molecular Biology, Cambridge. I/O subroutines modified by: Kevin Cowtan, University of York.