Calculate the number of waters in the first and second solvation shells based on distance critera.

watershell <solutemask> [out <filename>] [lower <lower cut>] [upper <upper cut>] [noimage] [<solventmask>]

<solutemask> Atom mask corresponding to solute of interest (required).
[out <filename>] Output file name.
[lower <lower cut>] Cutoff for the first water shell (default 3.4 Angstroms).
[upper <upper cut>] Cutoff for the second water shell (default 5.0 Angstroms).
[noimage] Do not image distances.
[<solventmask>] Optional atom mask corresponding to solvent.

DataSet Aspects:
[lower] Number of solvent molecules in first solvent shell.
[upper] Number of solvent molecules in second solvent shell.

This option will count the number of waters within a certain distance of the atoms in the <solutemask> in order to represent the first and second solvation shells. The optional <solventmask> can be used to consider other atoms as the solvent; the default is “:WAT”. This action is often used prior to the closest command in order to determine how many waters around a solute should be retained to maintain the first and/or second water shells.

As of version 17 this command is CUDA-enabled in CUDA versions of CPPTRAJ.