NAME
     CalcShift - calculate ring current shifts

SYNOPSIS
     CalcShift ( 1 | 0 ) ( 1 | 0) string expr expr

DESCRIPTION
     Calculate ring current and bond polarization shifts of
     all selected atoms, taking into account all
     rings/atoms of the same molecule.

     The first argument selects whether ring current shifts
     should be calculated, the second one whether bond
     polarization shifts should be calculated. At least one
     of the two should be selected, a warning is issued
     otherwise.

     The third argument gives the name of the model for the
     calculation. The description of the models is read
     from the file:

         $MOLMOLHOME/setup/RingShift

     The fourth argument selects a cutoff, contributions to
     the ring current shifts above this value are listed
     individually *before* the sum.

     The fifth argument gives a maximal distance for the
     atoms considered for the calculation of bond
     polarization shifts. Larger values will lead to longer
     calculation times.

     The results are listed for each molecule separately,
     a summary with average, minimal and maximal values is
     given at the end.

     For all protons but HN, a ring belonging to the same
     residue as the proton is not considered for the
     calculation of the ring current shift.

     The same is the case for the bond polarization: atoms
     of the same residue are not considred for the field
     calculation, except for HN atoms. A more elaborate
     strategy would have to be used to make the calculated
     numbers more useful as expected difference to random
     coil shift, especially for HN atoms.

EXAMPLE
     CalcShift 1 0 Heigh-Mallion 0.5 5.0

REFERENCE
     Case, DA.
     Calibration of ring-current effects in proteins and
     nucleic acids.
     Journal of Biomolecular NMR, 6 (1995) 341-346

WARNING
     The results for bond polarization shifts were not
     compared to the results of other programs, so there is
     no guarantee given on their correctness and usefulness.

SEE ALSO
     SelectAtom, PathNames

DATE
     960621
