11.5.4 Keywords for NMR Constraint Command

The purpose of the keywords is given in the following table:

UNIT

Unit number associated with the constraint file name (opened previously) If a UNIT number is not specified it is assumed that the constraints are to be read from the main input file.

FMAX

Maximum force for NOE constraints. This specifies the point in the constraint function when the function turns flatter, and the force begins to be reduced.

SLOPE

The constant force which applies to the outer region of the constraint function. This value should not be larger than FMAX.

NOEWEIGHT

The energy weight assigned to all NOE constraints read in after this point. This weight can also be set in the NOE constraint file.

JWEIGHT

The energy weight assigned to all J coupling constraints read in after this point. This weight can also be set in the NOE constraint file.

KJDIFF

The KJDIFF option sets the value of k' in the equation for V_d. The default value gives only two minima for the chi_1 torsion angle in the test case in the Constantine et al paper.

ECHO

If present, all lines read from the constraint file are echoed as they are read, and errors from searching atoms in the PSF will be printed.

JNORMALIZE

NOJNORMALIZE

This option controls the normalization of J constraint energy. The default state is normalization off. If it is turned on, then for single J's, CONGEN will calculate the value of E_j over all values of the torsion angle phi for each J separately, and it will normalize the energy calculations for each of the J's. In the case of joined J's, there are two possibilities. If the first three atoms or the last three atoms of joined J's are the same and the remaining atom is different, the program will assume that the J's represent the calculation of a prochiral group around an sp3 center. CONGEN will calculate the maximum of E_j over the range of the first torsion angle, with the second angle being set to 120 degrees plus the first angle. If the three atoms do not match, then the program will calculate the maximum of E_j over all possible values of the torsion angles for both J's. The grid size used for all these calculation is 2 degrees.

SUM

AVERAGE

NOAVERAGE

When the NOE constraints are specified, you can control whether constraints involving equivalent, degenerate, or non-stereospecifically assigned groups of protons are summed or averaged. The SUM and NOAVERAGE keyword specifies summing, the AVERAGE keyword specifies averaging. This specification will affect all succeeding constraints read in by the program.

CLEAR

Normally, the NMRC commands add constraints to the current lists. The CLEAR option will clear the named list before new ones are read in. If you specify NOE, then the NOE constraints are cleared, and if you specify JCOUPLING, then the J coupling constraints are cleared. Both of these keywords may be abbreviated to one letter, and you may specify multiple CLEAR options.

TITLE

NOTITLE

By default, a title, see See Syntactic Glossary, is read from any constraint file read from any unit other than the default command input. From unit 5, no title is required. These options can override that default behavior. TITLE specifies that a title will be read from the constraint file, and NOTITLE specifies that no title will be read.