BUMP s [0.1] d1 [#] d2 [#] d3 [#] ...'Antibumping' restraints are generated automatically for all (solvent water) atoms which have been flagged with CONN 0. The restraints can be generated between CONN 0 satoms and all other non-hydrogen atoms, and appear in ubsequent tables as DFIX instructions with negative d and effective standard deviation s. The values to be used for d are given in SFAC order as d1, d2, d3, ...; the default values are 3.2 for C, 2.7 for N, 2.6 for O and 3.5 for ALL other elements. If the structure contains atoms of other elements (e.g. explicit cations in polynucleotides) that can interact with the solvent, it will be necessary to specify the appropriate distances on the BUMP instruction. The restraints are also set up for all symmetry equivalents automatically; however if the sum of occupancies of the two atoms is less than 1.1, no restraint is generated. Iterative refinement with antibumping restraints, followed by deletion of atoms which persist in giving unacceptable distances or for which the (equivalent isotropic) displacement parameters become larger than say 1.0 to 1.2 A2, and insertion of new potential solvent atoms from difference electron density syntheses, provides a reliable procedure for building up a solvent model with acceptable hydrogen bonding distances which is consistent with the diffraction data; PLAN 200 2.3 would be appropriate. If there are more than 15 different SFAC ftypes, d15 is used or those with numbers greater than 15.
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