[gmx-users] Hydrogen bonding
sawit02 at student.sdu.dk
Wed Nov 18 00:23:48 CET 2009
I have done simulations of one small molecule that diffuses into a DMPC membrane. This small molecule contains an alcohol group and is therefore capable of hydrogen bonding to the oxygens of DMPC (phosphate and glycerol region).
I have read the manual (section 8.12 and g_hbond -h), searched the mailing list and google but I have not been able to find a more thorough description of the output possibilities than in the manual.
I have tried three different approaches:
1. The -OH group of the small molecule and the glycerol oxygens
2. The -OH group of the small molecule and the phosphate oxygens
3. The small molecule and DMPC (no subgroups)
No. 1 gives 38 hbond, no. 2 gives 15 hbonds and no. 3 gives 53 hbonds. So 1 + 2 = 3, which is fine.
Below is the output from no. 1: (gromacs 4.0.4)
Specify 2 groups to analyze:
Selected 0: 'O11_&_PALC_H12_&_PALC'
Selected 1: 'O7_&_DMPC_&_DMPC_O9_&_DMPC_O10_&_DMPC'
Checking for overlap in atoms between O11_&_PALC_H12_&_PALC and O7_&_DMPC_&_DMPC_O9_&_DMPC_O10_&_DMPC
Calculating hydrogen bonds between O11_&_PALC_H12_&_PALC (2 atoms) and O7_&_DMPC_&_DMPC_O9_&_DMPC_O10_&_DMPC (384 atoms)
Found 1 donors and 385 acceptors
Making hbmap structure...done.
Will do grid-seach on 15x15x24 grid, rcut=0.35
Found 15 different hydrogen bonds in trajectory
Found 23 different atom-pairs within hydrogen bonding distance
Merging hbonds with Acceptor and Donor swapped
- Reduced number of hbonds from 15 to 15
- Reduced number of distances from 23 to 23
Average number of hbonds per timeframe 0.083 out of 192.5 possible
What does these "15 different hydrogen bond in trajectory" mean? I don't understand this. I also don't understand "Average number of hbonds per timeframe 0.083 out of 192.5 possible" - 192.5 possible hbonds?? Can anyone shed some light on this?
Another question relates to the lifetime of the hbond calculated when the "-life" flag is given. The produced .xvg file contain three columns: time, p(t), and t p(t). What is p(t) and t p(t)? And how can I find the lifetime?
Thank you in advance,
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