| ## g_spol Main Table of Contents | VERSION 4.6 Sat 19 Jan 2013

### Description

`g_spol` analyzes dipoles around a solute; it is especially useful for polarizable water. A group of reference atoms, or a center of mass reference (option `-com`) and a group of solvent atoms is required. The program splits the group of solvent atoms into molecules. For each solvent molecule the distance to the closest atom in reference group or to the COM is determined. A cumulative distribution of these distances is plotted. For each distance between `-rmin` and `-rmax` the inner product of the distance vector and the dipole of the solvent molecule is determined. For solvent molecules with net charge (ions), the net charge of the ion is subtracted evenly from all atoms in the selection of each ion. The average of these dipole components is printed. The same is done for the polarization, where the average dipole is subtracted from the instantaneous dipole. The magnitude of the average dipole is set with the option `-dip`, the direction is defined by the vector from the first atom in the selected solvent group to the midpoint between the second and the third atom.

### Files

option | filename | type | description
--- | --- | --- | ---
`-f` | `traj.xtc` | Input | Trajectory: xtc trr trj gro g96 pdb cpt
`-s` | `topol.tpr` | Input | Run input file: tpr tpb tpa
`-n` | `index.ndx` | Input, Opt. | Index file
`-o` | `scdist.xvg` | Output | xvgr/xmgr file

### Other options

option | type | default | description
--- | --- | --- | ---
`-[no]h` | bool | `no` | Print help info and quit
`-[no]version` | bool | `no` | Print version info and quit
`-nice` | int | `19` | Set the nicelevel
`-b` | time | `0` | First frame (ps) to read from trajectory
`-e` | time | `0` | Last frame (ps) to read from trajectory
`-dt` | time | `0` | Only use frame when t MOD dt = first time (ps)
`-[no]w` | bool | `no` | View output `.xvg`, `.xpm`, `.eps` and `.pdb` files
`-xvg` | enum | `xmgrace` | xvg plot formatting: `xmgrace`, `xmgr` or `none`
`-[no]com` | bool | `no` | Use the center of mass as the reference postion
`-refat` | int | `1` | The reference atom of the solvent molecule
`-rmin` | real | `0` | Maximum distance (nm)
`-rmax` | real | `0.32` | Maximum distance (nm)
`-dip` | real | `0` | The average dipole (D)
`-bw` | real | `0.01` | The bin width

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