| 
 | VERSION 3.3.1 | 
g_velacc computes the velocity autocorrelation function. When the -s option is used, the momentum autocorrelation function is calculated.
With option -mol the momentum autocorrelation function of molecules is calculated. In this case the index group should consist of molecule numbers instead of atom numbers.
| option | filename | type | description | 
|---|---|---|---|
| -f | traj.trr | Input | Full precision trajectory: trr trj | 
| -s | topol.tpr | Input, Opt. | Structure+mass(db): tpr tpb tpa gro g96 pdb xml | 
| -n | index.ndx | Input, Opt. | Index file | 
| -o | vac.xvg | Output | xvgr/xmgr file | 
| option | type | default | description | 
|---|---|---|---|
| -[no]h | bool | no | Print help info and quit | 
| -nice | int | 19 | Set the nicelevel | 
| -b | time | 0 | First frame (ps) to read from trajectory | 
| -e | time | 0 | Last frame (ps) to read from trajectory | 
| -dt | time | 0 | Only use frame when t MOD dt = first time (ps) | 
| -[no]w | bool | no | View output xvg, xpm, eps and pdb files | 
| -[no]xvgr | bool | yes | Add specific codes (legends etc.) in the output xvg files for the xmgrace program | 
| -[no]mol | bool | no | Calculate vac of molecules | 
| -acflen | int | -1 | Length of the ACF, default is half the number of frames | 
| -[no]normalize | bool | yes | Normalize ACF | 
| -P | enum | 0 | Order of Legendre polynomial for ACF (0 indicates none): 0, 1, 2 or 3 | 
| -fitfn | enum | none | Fit function: none, exp, aexp, exp_exp, vac, exp5, exp7 or exp9 | 
| -ncskip | int | 0 | Skip N points in the output file of correlation functions | 
| -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 till the end |