Thanks a lot, Erik!
But could you specify how to build the index of water in certain region,
say 0<z<2nm? It seems that make_ndx can't do that.
On 05/23/2011 11:05 AM, Erik Marklund wrote:
Baofu Qiao skrev 2011-05-23 10.47:
Hi all,
Very recently, I meet a problem when using g_hbond (gromacs 4.5.3
with the bugfixed)
*********************************
Select a group: Selected 1: 'SOL'
Select a group: Selected 1: 'SOL'
Calculating hydrogen bonds in SOL (98280 atoms)
Found 32760 donors and 32760 acceptors
*Segmentation fault*
*********************************
I check the code of gmx_hbond.c. The problem comes from the function
of "mk_hbmap". However, g_hbond doesn't complain
"gmx_fatal(FARGS,"Could not allocate enough memory for hbmap")' while
giving the "Segmentation fault". My first guess is 1) the function
doesn't work correctly; 2) there is no enough memory for 32760 donors
and 32760 acceptors.
What I really want to calculate is the HB correlation function is
some slab structure of thickness of about 3ns, where there is only
~3000 waters. Can someone give me some suggestions? Thanks a lot!
best regards,
Baofu Qiao
That sounds like a memory problem indeed, and it could be outside the
control of g_hbond. From the manpages of malloc:
"By default, Linux follows an optimistic memory allocation
strategy. This means that when malloc() returns non-NULL there is
no guarantee that the memory really is available. This is a really bad
bug."
g_hbond checks for NULL pointers to decide whether snew() was
successful or not. Hence the menetioned bug could be the culprit. That
said, the hbmap of your system requires 32760^2 pointers (> 8 Gb on 64
bit systems) that in turn points to existence arrays with size that
scales with trajectory length. Hence you will easily run out of
memory. I suggest that you build the acf for a subset of your system,
e.g. 1000 waters. The acf will converge slower, but have the same
features. You can do this many times and take an average for better
statistics.
Cheers,
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