[gmx-users] Angle definition in g_hbond ...

[sharada]

dear gmx-users,
I have a very fundamental query. I am trying to obtain the backbone hydrogen bonds formed during a 15ns simulation of a 35 long protein. When I do this by using g_hbond and selecting the Backbone groups, I am getting no hydrogen bonds at all . However, when I plot the hydrogen bonds for some of the structures picked up through the dynamics  using InsightII  I am able to see the backbone  HBs in almost all of them. 
This is the command I am using: 
 g_hbond -f  HBD1_15npep.trr -s HBD1_5mr_md.tpr -n HBD1_10n_nsl.ndx -num hnum.xvg -g hb.log
this is the output I obtain and the hb.log file is not created :
Reading file HBD1_5mr_md.tpr, VERSION 3.3 (single precision)
Specify 2 groups to analyze:
Group     0 (     Protein) has   358 elements
Group     1 (   Protein-H) has   271 elements
Group     2 (     C-alpha) has    36 elements
Group     3 (    Backbone) has   108 elements
Group     4 (   MainChain) has   144 elements
Group     5 (MainChain+Cb) has   177 elements
Group     6 ( MainChain+H) has   181 elements
Group     7 (   SideChain) has   177 elements
Group     8 ( SideChain-H) has   126 elements
Group     9 ( Prot-Masses) has   358 elements
Select a group: 3
Selected 4: 'Backbone'
Select a group: 3
Selected 4: 'Backbone'
Calculating hydrogen bonds in Backbone (108 atoms)
Found 0 donors and 72 acceptors
No Donors found
-------------------------------------------------------
Program g_hbond, VERSION 3.3
Source code file: gmx_hbond.c, line: 1827
Fatal error:
Nothing to be done
-------------------------------------------------------
"Keep Your Shoes and Socks On, People" (F. Zappa)
 Could anyone  please let me know the distance and angle definition used in the program g_hbond. There is a mention about cutoff angle and Cutoff radius as shown below. 
          -a   real     30  Cutoff angle (degrees, Donor - Hydrogen -
                            Acceptor)
          -r   real   0.35  Cutoff radius (nm, X - Acceptor, see next option)
What exactly is the Cutoff angle ?  Usually the angle of Donor - Hydrogen -Acceptor  is around 120 degrees and the distance is around 0.2nm. I have searched the gromacs forum but could not get any help.  thanks for your patience reading. 
sharada
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