CHARMM c28a3 lonepair.doc

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                            Lone Pair Facility

      This routine parses the lone-pair command which converts existing
atoms to lone-pairs in the PSF.

                     Bernard R. Brooks, NIH, October, 1997

* Menu:

* Syntax::                 Syntax of the lone-pair command
* Description::            Description of the lone-pair facility

File: LonePair ]-[ Node: Syntax
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                    Syntax of the Lone-Pait Command


LONEpair { FIXEd   atom-spec   [ xloc-yloc-zloc ]            } [MASS]
         {                                                   }
         { CENTer  atom-spec  {  atom-selection   }          }
         {                    { repeat(atom-spec) }          }
         {                                                   }
         { COLOcate { 2x(atom-selection) }                   } 
         {          { 2x(atom-spec)      }                   } 
         {                                                   }
         { { COLInear distance-spec } { 3x(atom-selection) } }
         { { CEN2                   } { 3x(atom-spec)      } }
         {                                                   }
         { { RELAtive } { 4x(atom-selection) } position-spec }
         { { BISEctor } { 4x(atom-selection) }               }
         { { CEN3     }                                      }
         {                                                   }
         { PRINt                                             }
         { CLEAr                                             }

atom-spec::= { residue-number atom-name }
             { segid  resid atom-name   }
             { BYNUm  atom-number       }

atom-selection ::= see *note select:(select.doc).

xloc-yloc-zloc::= three real numbers identifying the new position

distance-spec::= [DISTance real] [SCAled real]
                   (def 0.0)       (def 0.0)

postition-spec::= [DISTance real] [ANGLe real] [DIHEdral real]
                     (def 0.0)      (def 0.0)    (def 0.0)

File: LonePair ]-[ Node: Description
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                    Note on the lone-pair command

1.  The "LONEpair FIXEd" command places atoms that are fixed in
the unit cell fractional coordinates.  If running constant pressure,
these atoms will move in response to the changes in the box size/shape.
Thus, this is different than "CONStraint FIX".  The specified position
is in cartesian space (Angstroms).

2.  The "LONEpair CENTer" command places a single particle at the
weighted center of all the subsequently specified atoms (either by
atom-selection or atom-spec).

3. For all commands employing multiple atom selections, each atom
then matched off in sequential order.  The first atom selection is
the list of lonepair atoms.  This is intended to make it easy
to create a large number of TIP4P water molecules with one command:

    LONEpair BISEctor DIST 0.15 ANGLE 0.0 DIHE 0.0 -
                         SELE ATOM SOLV * OM  END - 
                         SELE ATOM SOLV * OH2 END - 
                         SELE ATOM SOLV * H1  END - 
                         SELE ATOM SOLV * H2  END

This assumes that all of the residues in the segment SOLV are TIP4P
types.  It places the atom OM (with zero mass) at a point 0.15 A
from the atom OH2 in the direction of the H1-H2 bisector.

4. The MASS option is used in the CEN* commands to determine how the
center position is computed.  The default is to use the center of
geometry (unit weights for all atoms).

5. The CLEAr command will remove all lone-pairs from the PSF and
resets the lone-pair facility.  WARNING:  The masses of old lone-pairs
will still be zero.  These need to me modified "SCALAR MASS SET..."
before running further dynamics.

6.  Lone-pair atoms may have other lone-pair atoms as a host, provided
that the host is not already a lonepair.  In other words, you can define
the postition of lone-pair B based on the postition of lone-pair A
ONLY if lonepair B is define before lonepair A.  ORDER IS IMPORTANT!!

7.  The LONEpair command sets the MASS to zero of all selected
lone-pairs.  This MAY change the total mass of the system.  The
lost mass is NOT added to any other atom.

8.  For the BISEctor option, the dihedral is based on: I,J,(K+L)/2,L
where I,J,K,L are the coordinate vectors of the specified atoms.

9.  For the COLInear option, the DISTance value is a signed value
of the distance from the first host AWAY from the second host.
The SCALed value is a relative distance from the first atoms AWAY
from the second atom (a SCALed factor of -1.0 will put the lonepair
at the position of the second atom).  For example, the following
two commands do exactly the same thing:
    LONEpair COLINEAR DIST 0.0 SCALE -0.5  -
             SELE type HB  END SELE type H1  END SELE type H2  END
    LONEpair CEN2  - 
             SELE type HB  END SELE type H1  END SELE type H2  END

10. When running CHARMM in parallel, the lonepair atom should be in
the same group as ALL of its hosts in order to ensure that these
atoms are all in the same parallel partition.  THIS IS NOT CHECKED!

11. Lonepair data is considered to be part of the PSF.  When a PSF
with lonepairs is read from a file, the lonepair facility is also
read (or appended).

12. When using lonepairs with PERT, both PSF's MUST have the same
lonepair data.  In other words, you cannot perturb a lonepair into
a non-lonepair.

13. At present, there is no way to specify lonepair information in
an RTF file, and thus lonepairs cannot be setup in the generation
process (expect the old ST2 water lonepairs).  This will change if
there is demand.

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NIH/DCRT/Laboratory for Structural Biology
FDA/CBER/OVRR Biophysics Laboratory
Modified, updated and generalized by C.L. Brooks, III
The Scripps Research Institute