Man page - gmx-dipoles(1)

Packages contains this manual

Manual

GMX-DIPOLES

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
SEE ALSO
COPYRIGHT

NAME

gmx-dipoles - Compute the total dipole plus fluctuations

SYNOPSIS

gmx dipoles [ -en [<.edr>] ] [ -f [<.xtc/.trr/...>] ] [ -s [<.tpr>] ]
[ -n [<.ndx>] ] [ -o [<.xvg>] ] [ -eps [<.xvg>] ] [ -a [<.xvg>] ]
[ -d [<.xvg>] ] [ -c [<.xvg>] ] [ -g [<.xvg>] ]
[ -adip [<.xvg>] ] [ -dip3d [<.xvg>] ] [ -cos [<.xvg>] ]
[ -cmap [<.xpm>] ] [ -slab [<.xvg>] ] [ -b <time> ] [ -e <time> ]
[ -dt <time> ] [ -[no]w ] [ -xvg <enum> ] [ -mu <real> ]
[ -mumax <real> ] [ -epsilonRF <real> ] [ -skip <int> ]
[ -temp <real> ] [ -corr <enum> ] [ -[no]pairs ] [ -[no]quad ]
[ -ncos <int> ] [ -axis <string> ] [ -sl <int> ]
[ -gkratom <int> ] [ -gkratom2 <int> ] [ -rcmax <real> ]
[ -[no]phi ] [ -nlevels <int> ] [ -ndegrees <int> ]
[ -acflen <int> ] [ -[no]normalize ] [ -P <enum> ]
[ -fitfn <enum> ] [ -beginfit <real> ] [ -endfit <real> ]

DESCRIPTION

gmx dipoles computes the total dipole plus fluctuations of a simulation system. From this you can compute e.g. the dielectric constant for low-dielectric media. For molecules with a net charge, the net charge is subtracted at center of mass of the molecule.

The file Mtot.xvg contains the total dipole moment of a frame, the components as well as the norm of the vector. The file aver.xvg contains <|mu|ˆ2> and |<mu>|ˆ2 during the simulation. The file dipdist.xvg contains the distribution of dipole moments during the simulation The value of -mumax is used as the highest value in the distribution graph.

Furthermore, the dipole autocorrelation function will be computed when option -corr is used. The output file name is given with the -c option. The correlation functions can be averaged over all molecules ( mol ), plotted per molecule separately ( molsep ) or it can be computed over the total dipole moment of the simulation box ( total ).

Option -g produces a plot of the distance dependent Kirkwood G-factor, as well as the average cosine of the angle between the dipoles as a function of the distance. The plot also includes gOO and hOO according to Nymand & Linse, J. Chem. Phys. 112 (2000) pp 6386-6395. In the same plot, we also include the energy per scale computed by taking the inner product of the dipoles divided by the distance to the third power.

EXAMPLES

gmx dipoles -corr mol -P 1 -o dip_sqr -mu 2.273 -mumax 5.0

This will calculate the autocorrelation function of the molecular dipoles using a first order Legendre polynomial of the angle of the dipole vector and itself a time t later. For this calculation 1001 frames will be used. Further, the dielectric constant will be calculated using an -epsilonRF of infinity (default), temperature of 300 K (default) and an average dipole moment of the molecule of 2.273 (SPC). For the distribution function a maximum of 5.0 will be used.

OPTIONS

Options to specify input files:
-en [<.edr>] (ener.edr) (Optional)

Energy file

-f [<.xtc/.trr/...>] (traj.xtc)

Trajectory: xtc trr cpt gro g96 pdb tng

-s [<.tpr>] (topol.tpr)

Portable xdr run input file

-n [<.ndx>] (index.ndx) (Optional)

Index file

Options to specify output files:
-o [<.xvg>] (Mtot.xvg)

xvgr/xmgr file

-eps [<.xvg>] (epsilon.xvg)

xvgr/xmgr file

-a [<.xvg>] (aver.xvg)

xvgr/xmgr file

-d [<.xvg>] (dipdist.xvg)

xvgr/xmgr file

-c [<.xvg>] (dipcorr.xvg) (Optional)

xvgr/xmgr file

-g [<.xvg>] (gkr.xvg) (Optional)

xvgr/xmgr file

-adip [<.xvg>] (adip.xvg) (Optional)

xvgr/xmgr file

-dip3d [<.xvg>] (dip3d.xvg) (Optional)

xvgr/xmgr file

-cos [<.xvg>] (cosaver.xvg) (Optional)

xvgr/xmgr file

-cmap [<.xpm>] (cmap.xpm) (Optional)

X PixMap compatible matrix file

-slab [<.xvg>] (slab.xvg) (Optional)

xvgr/xmgr file

Other options:
-b <time> (0)

Time of first frame to read from trajectory (default unit ps)

-e <time> (0)

Time of last frame to read from trajectory (default unit ps)

-dt <time> (0)

Only use frame when t MOD dt = first time (default unit ps)

-[no]w (no)

View output .xvg , .xpm , .eps and .pdb files

-xvg <enum> (xmgrace)

xvg plot formatting: xmgrace, xmgr, none

-mu <real> (-1)

dipole of a single molecule (in Debye)

-mumax <real> (5)

max dipole in Debye (for histogram)

-epsilonRF <real> (0)

epsilon of the reaction field used during the simulation, needed for dielectric constant calculation. WARNING: 0.0 means infinity (default)

-skip <int> (0)

Skip steps in the output (but not in the computations)

-temp <real> (300)

Average temperature of the simulation (needed for dielectric constant calculation)

-corr <enum> (none)

Correlation function to calculate: none, mol, molsep, total

-[no]pairs (yes)

Calculate |cos(theta)| between all pairs of molecules. May be slow

-[no]quad (no)

Take quadrupole into account

-ncos <int> (1)

Must be 1 or 2. Determines whether the <cos(theta)> is computed between all molecules in one group, or between molecules in two different groups. This turns on the -g flag.

-axis <string> (Z)

Take the normal on the computational box in direction X, Y or Z.

-sl <int> (10)

Divide the box into this number of slices.

-gkratom <int> (0)

Use the n-th atom of a molecule (starting from 1) to calculate the distance between molecules rather than the center of charge (when 0) in the calculation of distance dependent Kirkwood factors

-gkratom2 <int> (0)

Same as previous option in case ncos = 2, i.e. dipole interaction between two groups of molecules

-rcmax <real> (0)

Maximum distance to use in the dipole orientation distribution (with ncos == 2). If zero, a criterion based on the box length will be used.

-[no]phi (no)

Plot the 'torsion angle' defined as the rotation of the two dipole vectors around the distance vector between the two molecules in the .xpm file from the -cmap option. By default the cosine of the angle between the dipoles is plotted.

-nlevels <int> (20)

Number of colors in the cmap output

-ndegrees <int> (90)

Number of divisions on the y -axis in the cmap output (for 180 degrees)

-acflen <int> (-1)

Length of the ACF, default is half the number of frames

-[no]normalize (yes)

Normalize ACF

-P <enum> (0)

Order of Legendre polynomial for ACF (0 indicates none): 0, 1, 2, 3

-fitfn <enum> (none)

Fit function: none, exp, aexp, exp_exp, exp5, exp7, exp9

-beginfit <real> (0)

Time where to begin the exponential fit of the correlation function

-endfit <real> (-1)

Time where to end the exponential fit of the correlation function, -1 is until the end

SEE ALSO

gmx(1)

More information about GROMACS is available at <- http://www.gromacs.org/ >.

COPYRIGHT

2025, GROMACS development team