GMX-GANGLE(1) GROMACS GMX-GANGLE(1)

# NAME¶

gmx-gangle - Calculate angles

# SYNOPSIS¶

```gmx gangle [-f [<.xtc/.trr/...>]] [-s [<.tpr/.gro/...>]] [-n [<.ndx>]]

[-oav [<.xvg>]] [-oall [<.xvg>]] [-oh [<.xvg>]]

[-b <time>] [-e <time>] [-dt <time>] [-tu <enum>]

[-fgroup <selection>] [-xvg <enum>] [-[no]rmpbc]

[-[no]pbc] [-sf <file>] [-selrpos <enum>]

[-seltype <enum>] [-g1 <enum>] [-g2 <enum>] [-binw <real>]

[-group1 <selection>] [-group2 <selection>]
```

# DESCRIPTION¶

gmx gangle computes different types of angles between vectors. It supports both vectors defined by two positions and normals of planes defined by three positions. The z axis or the local normal of a sphere can also be used as one of the vectors. There are also convenience options 'angle' and 'dihedral' for calculating bond angles and dihedrals defined by three/four positions.

The type of the angle is specified with -g1 and -g2. If -g1 is angle or dihedral, -g2 should not be specified. In this case, -group1 should specify one or more selections, and each should contain triplets or quartets of positions that define the angles to be calculated.

If -g1 is vector or plane, -group1 should specify selections that contain either pairs (vector) or triplets (plane) of positions. For vectors, the positions set the endpoints of the vector, and for planes, the three positions are used to calculate the normal of the plane. In both cases, -g2 specifies the other vector to use (see below).

With -g2 vector or -g2 plane, -group2 should specify another set of vectors. -group1 and -group2 should specify the same number of selections. It is also allowed to only have a single selection for one of the options, in which case the same selection is used with each selection in the other group. Similarly, for each selection in -group1, the corresponding selection in -group2 should specify the same number of vectors or a single vector. In the latter case, the angle is calculated between that single vector and each vector from the other selection.

With -g2 sphnorm, each selection in -group2 should specify a single position that is the center of the sphere. The second vector is calculated as the vector from the center to the midpoint of the positions specified by -group1.

With -g2 z, -group2 is not necessary, and angles between the first vectors and the positive Z axis are calculated.

With -g2 t0, -group2 is not necessary, and angles are calculated from the vectors as they are in the first frame.

There are three options for output: -oav writes an xvg file with the time and the average angle for each frame. -oall writes all the individual angles. -oh writes a histogram of the angles. The bin width can be set with -binw. For -oav and -oh, separate average/histogram is computed for each selection in -group1.

# OPTIONS¶

Options to specify input files:

Input trajectory or single configuration: xtc trr cpt gro g96 pdb tng
Input structure: tpr gro g96 pdb brk ent
Extra index groups

Options to specify output files:

Average angles as a function of time
All angles as a function of time
Histogram of the angles

Other options:

First frame (ps) to read from trajectory
Last frame (ps) to read from trajectory
Only use frame if t MOD dt == first time (ps)
Unit for time values: fs, ps, ns, us, ms, s
Atoms stored in the trajectory file (if not set, assume first N atoms)
Plot formatting: none, xmgrace, xmgr
-[no]rmpbc (yes)
Make molecules whole for each frame
-[no]pbc (yes)
Use periodic boundary conditions for distance calculation
Provide selections from files
Selection reference positions: atom, res_com, res_cog, mol_com, mol_cog, whole_res_com, whole_res_cog, whole_mol_com, whole_mol_cog, part_res_com, part_res_cog, part_mol_com, part_mol_cog, dyn_res_com, dyn_res_cog, dyn_mol_com, dyn_mol_cog
Default selection output positions: atom, res_com, res_cog, mol_com, mol_cog, whole_res_com, whole_res_cog, whole_mol_com, whole_mol_cog, part_res_com, part_res_cog, part_mol_com, part_mol_cog, dyn_res_com, dyn_res_cog, dyn_mol_com, dyn_mol_cog
Type of analysis/first vector group: angle, dihedral, vector, plane
Type of second vector group: none, vector, plane, t0, z, sphnorm
Binwidth for -oh in degrees
First analysis/vector selection
Second analysis/vector selection

gmx(1)

2021, GROMACS development team

 March 29, 2021 2020.6-Debian-2020.6-2