1 .TH g_spatial 1 "Mon 4 Apr 2011" "" "GROMACS suite, VERSION 4.5.4-dev-20110404-bc5695c"
3 g_spatial - calculates the spatial distribution function
5 .B VERSION 4.5.4-dev-20110404-bc5695c
8 .BI "\-s" " topol.tpr "
10 .BI "\-n" " index.ndx "
12 .BI "\-[no]version" ""
24 \&\fB g_spatial\fR calculates the spatial distribution function and
25 \&outputs it in a form that can be read by VMD as Gaussian98 cube format.
26 \&This was developed from template.c (GROMACS\-3.3).
27 \&For a system of 32,000 atoms and a 50 ns trajectory, the SDF can be generated
28 \&in about 30 minutes, with most of the time dedicated to the two runs through
29 \&\fB trjconv\fR that are required to center everything properly.
30 \&This also takes a whole bunch of space (3 copies of the \fB .xtc\fR file).
31 \&Still, the pictures are pretty and very informative when the fitted selection is properly made.
32 \&3\-4 atoms in a widely mobile group (like a free amino acid in solution) works
33 \&well, or select the protein backbone in a stable folded structure to get the SDF
34 \&of solvent and look at the time\-averaged solvation shell.
35 \&It is also possible using this program to generate the SDF based on some arbitrary
36 \&Cartesian coordinate. To do that, simply omit the preliminary \fB trjconv\fR steps.
40 \&1. Use \fB make_ndx\fR to create a group containing the atoms around which you want the SDF
42 \&2. \fB trjconv \-s a.tpr \-f a.xtc \-o b.xtc \-center tric \-ur compact \-pbc none\fR
44 \&3. \fB trjconv \-s a.tpr \-f b.xtc \-o c.xtc \-fit rot+trans\fR
46 \&4. run \fB g_spatial\fR on the \fB .xtc\fR output of step 3.
48 \&5. Load \fB grid.cube\fR into VMD and view as an isosurface.
50 \&\fB Note\fR that systems such as micelles will require \fB trjconv \-pbc cluster\fR between steps 1 and 2
54 \&The SDF will be generated for a cube that contains all bins that have some non\-zero occupancy.
55 \&However, the preparatory \fB \-fit rot+trans\fR option to \fB trjconv\fR implies that your system will be rotating
56 \&and translating in space (in order that the selected group does not). Therefore the values that are
57 \&returned will only be valid for some region around your central group/coordinate that has full overlap
58 \&with system volume throughout the entire translated/rotated system over the course of the trajectory.
59 \&It is up to the user to ensure that this is the case.
63 \&When the allocated memory is not large enough, a segmentation fault may occur. This is usually detected
64 \&and the program is halted prior to the fault while displaying a warning message suggesting the use of the \fB \-nab\fR (Number of Additional Bins)
65 \&option. However, the program does not detect all such events. If you encounter a segmentation fault, run it again
66 \&with an increased \fB \-nab\fR value.
70 \&To reduce the amount of space and time required, you can output only the coords
71 \&that are going to be used in the first and subsequent run through \fB trjconv\fR.
72 \&However, be sure to set the \fB \-nab\fR option to a sufficiently high value since
73 \&memory is allocated for cube bins based on the initial coordinates and the \fB \-nab\fR
77 .BI "\-s" " topol.tpr"
79 Structure+mass(db): tpr tpb tpa gro g96 pdb
83 Trajectory: xtc trr trj gro g96 pdb cpt
85 .BI "\-n" " index.ndx"
91 Print help info and quit
93 .BI "\-[no]version" "no "
94 Print version info and quit
96 .BI "\-nice" " int" " 0"
99 .BI "\-b" " time" " 0 "
100 First frame (ps) to read from trajectory
102 .BI "\-e" " time" " 0 "
103 Last frame (ps) to read from trajectory
105 .BI "\-dt" " time" " 0 "
106 Only use frame when t MOD dt = first time (ps)
109 View output \fB .xvg\fR, \fB .xpm\fR, \fB .eps\fR and \fB .pdb\fR files
111 .BI "\-[no]pbc" "no "
112 Use periodic boundary conditions for computing distances
114 .BI "\-[no]div" "yes "
115 Calculate and apply the divisor for bin occupancies based on atoms/minimal cube size. Set as TRUE for visualization and as FALSE (\fB \-nodiv\fR) to get accurate counts per frame
117 .BI "\-ign" " int" " \-1"
118 Do not display this number of outer cubes (positive values may reduce boundary speckles; \-1 ensures outer surface is visible)
120 .BI "\-bin" " real" " 0.05 "
121 Width of the bins in nm
123 .BI "\-nab" " int" " 4"
124 Number of additional bins to ensure proper memory allocation
129 More information about \fBGROMACS\fR is available at <\fIhttp://www.gromacs.org/\fR>.