VelocityCylinder#
- class maicos.modules.velocitycylinder.VelocityCylinder(atomgroups, dim=2, zmin=None, zmax=None, bin_width=1, rmin=0, rmax=None, refgroup=None, grouping='atoms', unwrap=True, bin_method='com', output='velocity.dat', concfreq=0, vdim=0, flux=False)[source]#
Bases:
ProfileCylinderBase
Compute the cartesian velocity profile across a cylinder.
Reads in coordinates and velocities from a trajectory and calculates a velocity \([\mathrm{Å/ps}]\) or a flux per unit area \([\mathrm{Å^{-2}\,ps^{-1}}]\) profile along a given axis.
The
grouping
keyword gives you fine control over the velocity profile, e.g., you can choose atomar or molecular velocities. Note, that if the first one is employed for complex compounds, usually a contribution corresponding to the vorticity appears in the profile.- Parameters:
atomgroups (list[AtomGroup]) – a list of
AtomGroup
objects for which the calculations are performed.refgroup (AtomGroup) –
Reference
AtomGroup
used for the calculation.If refgroup is provided, the calculation is performed relative to the center of mass of the AtomGroup.
If refgroup is
None
the calculations are performed to the center of the (changing) box.unwrap (bool) –
When
unwrap = True
, molecules that are broken due to the periodic boundary conditions are made whole.If the input contains molecules that are already whole, speed up the calculation by disabling unwrap. To do so, use the flag
-no-unwrap
when using MAICoS from the command line, or useunwrap = False
when using MAICoS from the Python interpreter.Note: Molecules containing virtual sites (e.g. TIP4P water models) are not currently supported in MDAnalysis. In this case, you need to provide unwrapped trajectory files directly, and disable unwrap. Trajectories can be unwrapped, for example, using the
trjconv
command of GROMACS.concfreq (int) – When concfreq (for conclude frequency) is larger than 0, the conclude function is called and the output files are written every concfreq frames
dim (int) – Dimension for binning (
x=0
,y=1
,z=2
).zmin (float) –
Minimal coordinate for evaluation (in Å) with respect to the center of mass of the refgroup.
If
zmin=None
, all coordinates down to the lower cell boundary are taken into account.zmax (float) –
Maximal coordinate for evaluation (in Å) with respect to the center of mass of the refgroup.
If
zmax = None
, all coordinates up to the upper cell boundary are taken into account.jitter (float) –
If
jitter is not None
, random numbers of the order of jitter (Å) are added to the atom positions.The appilication of a jitter is rationalized in possible aliasing effects when histogramming data, i.e., for spatial profiles. These aliasing effects can be stabilized with the application of a numerical jitter. The jitter value should be about the precision of the trajectory and will not alter the results of the histogram.
You can estimate the precision of the positions in your trajectory with
maicos.lib.util.trajectory_precision()
. Note that if the precision is not the same for all frames, the smallest precision should be used.bin_width (float) – Width of the bins (in Å).
rmin (float) – Minimal radial coordinate relative to the center of mass of the refgroup for evaluation (in Å).
rmax (float) –
Maximal radial coordinate relative to the center of mass of the refgroup for evaluation (in Å).
If
rmax=None
, the box extension is taken.grouping (str {
'atoms'
,'residues'
,'segments'
,'molecules'
,'fragments'
}) –Atom grouping for the calculations of profiles.
The possible grouping options are the atom positions (in the case where
grouping='atoms'
) or the center of mass of the specified grouping unit (in the case wheregrouping='residues'
,'segments'
,'molecules'
or'fragments'
).bin_method (str {
'cog'
,'com'
,'coc'
}) –Method for the position binning.
The possible options are center of geometry (
cog
), center of mass (com
), and center of charge (coc
).output (str) – Output filename.
vdim (int {0, 1, 2},) – Dimension for velocity binning (x=0, y=1, z=2).
flux (bool,) – Calculate the flux instead of the velocity \([Å^2/\mathrm{ps}]\).
- results.bin_pos#
Bin positions (in Å) ranging from
rmin
tormax
.- Type:
- results.profile#
Calculated profile.
- Type:
- results.dprofile#
Estimated profile’s uncertainity.
- Type: