1GMX-VELACC(1) GROMACS GMX-VELACC(1)
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6 gmx-velacc - Calculate velocity autocorrelation functions
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9 gmx velacc [-f [<.trr/.cpt/...>]] [-s [<.tpr/.gro/...>]] [-n [<.ndx>]]
10 [-o [<.xvg>]] [-os [<.xvg>]] [-b <time>] [-e <time>]
11 [-dt <time>] [-[no]w] [-xvg <enum>] [-[no]m] [-[no]recip]
12 [-[no]mol] [-acflen <int>] [-[no]normalize] [-P <enum>]
13 [-fitfn <enum>] [-beginfit <real>] [-endfit <real>]
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16 gmx velacc computes the velocity autocorrelation function. When the -m
17 option is used, the momentum autocorrelation function is calculated.
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19 With option -mol the velocity autocorrelation function of molecules is
20 calculated. In this case the index group should consist of molecule
21 numbers instead of atom numbers.
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23 By using option -os you can also extract the estimated (vibrational)
24 power spectrum, which is the Fourier transform of the velocity autocor‐
25 relation function. Be sure that your trajectory contains frames with
26 velocity information (i.e. nstvout was set in your original .mdp file),
27 and that the time interval between data collection points is much
28 shorter than the time scale of the autocorrelation.
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31 Options to specify input files:
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33 -f [<.trr/.cpt/...>] (traj.trr)
34 Full precision trajectory: trr cpt tng
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36 -s [<.tpr/.gro/...>] (topol.tpr) (Optional)
37 Structure+mass(db): tpr gro g96 pdb brk ent
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39 -n [<.ndx>] (index.ndx) (Optional)
40 Index file
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42 Options to specify output files:
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44 -o [<.xvg>] (vac.xvg)
45 xvgr/xmgr file
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47 -os [<.xvg>] (spectrum.xvg) (Optional)
48 xvgr/xmgr file
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50 Other options:
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52 -b <time> (0)
53 Time of first frame to read from trajectory (default unit ps)
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55 -e <time> (0)
56 Time of last frame to read from trajectory (default unit ps)
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58 -dt <time> (0)
59 Only use frame when t MOD dt = first time (default unit ps)
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61 -[no]w (no)
62 View output .xvg, .xpm, .eps and .pdb files
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64 -xvg <enum> (xmgrace)
65 xvg plot formatting: xmgrace, xmgr, none
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67 -[no]m (no)
68 Calculate the momentum autocorrelation function
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70 -[no]recip (yes)
71 Use cm^-1 on X-axis instead of 1/ps for spectra.
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73 -[no]mol (no)
74 Calculate the velocity acf of molecules
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76 -acflen <int> (-1)
77 Length of the ACF, default is half the number of frames
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79 -[no]normalize (yes)
80 Normalize ACF
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82 -P <enum> (0)
83 Order of Legendre polynomial for ACF (0 indicates none): 0, 1,
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86 -fitfn <enum> (none)
87 Fit function: none, exp, aexp, exp_exp, exp5, exp7, exp9
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89 -beginfit <real> (0)
90 Time where to begin the exponential fit of the correlation func‐
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93 -endfit <real> (-1)
94 Time where to end the exponential fit of the correlation func‐
95 tion, -1 is until the end
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98 gmx(1)
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100 More information about GROMACS is available at <‐
101 http://www.gromacs.org/>.
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104 2022, GROMACS development team
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1092022.3 Sep 02, 2022 GMX-VELACC(1)