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GHOST

Calculate the absolute position of a ghost atom with fixed coordinates in the local reference frame formed by three atoms. The computed ghost atom is stored as a virtual atom that can be accessed in an atom list through the the label for the GHOST action that creates it.

The atoms involved can be specified using
ATOMS the list of atoms which are involved the virtual atom's definition
COORDINATES coordinates of the ghost atom in the local reference frame
Examples
The following input instructs plumed to print the distance between the ghost atom and the center of mass for atoms 15,20:
GHOST ATOMS=1,5,10 COORDINATES=10.0,10.0,10.0 LABEL=c1
COM ATOMS=15,20       LABEL=c2
DISTANCE ATOMS=c1,c2  LABEL=d1
PRINT ARG=d1
(See also DISTANCE and PRINT).
Warning
If a force is added to a ghost atom, the contribution to the virial could contain small artifacts. It is therefore discouraged to use GHOST in a constant pressure simulation.