[gmx-users] meaning of results of g_hbond -ac

2013-07-17 Thread Wu Chaofu
Dear gmxers,
By running the command g_hbond -ac, a resulting .xvg file is generated,
which is attached below. In that file, there are five columns. I guess
that, the first column is time, the second the HB autocorrelation function.
But what are the other columns denoted by s1, s2, s3? Thanks a lot for any
reply.
Yours sincerely,
Chaofu Wu

# This file was created Wed Jul 17 09:49:34 2013
# by the following command:
# g_hbond -f iconf.xtc -s conf.tpr -n -ac ihbac2.xvg
#
# g_hbond is part of G R O M A C S:
#
# GROtesk MACabre and Sinister
#
@title "Hydrogen Bond Autocorrelation"
@xaxis  label "Time (ps)"
@yaxis  label "C(t)"
@TYPE xy
@ view 0.15, 0.15, 0.75, 0.85
@ legend on
@ legend box on
@ legend loctype view
@ legend 0.78, 0.8
@ legend length 2
@ s0 legend "Ac\sfin sys\v{}\z{}(t)"
@ s1 legend "Ac(t)"
@ s2 legend "Cc\scontact,hb\v{}\z{}(t)"
@ s3 legend "-dAc\sfs\v{}\z{}/dt"
 0   1   1  -5.79228e-110.902311
 1   0.09955770.1001860.1345570.455234
 2   0.0895326   0.09016760.126435  0.00815676
 3   0.0832442   0.08388360.123311  0.00541426
 4   0.0787041   0.07934660.117936  0.00376486
 5   0.0757145   0.07635910.116489  0.00198866
 6   0.0747267   0.07537210.112655  0.00177937
 7   0.0721557   0.07280290.109565  0.00255146
 8   0.0696238   0.07027270.107288  0.00241577
 9   0.0673242   0.06797470.106287  0.00157028
10   0.0664832   0.06713430.104746   0.0014926
110.064339   0.06499160.101947  0.00148105
12   0.0635211   0.0641743   0.0991141  0.00131835
13   0.0617023   0.06235670.101322  0.00147757
140.060566   0.0612212   0.0965892  0.000719808
.
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[gmx-users] How to modify the code g_hbond to analyze the non-traditional hydrogen bonds like C-H...O

2013-06-30 Thread Wu Chaofu
Dear gmxers,
I want to analyze the non-traditional hydrogen bonds like C-H...O. To my
best knowledge, the g_hbond code can be used for traditional hydrogen bonds
but not for our case. One possible solution is to modify the g_hbond code
to include the non-traditional hydrogen bonds. However, the code is too
long and too complex to understand for me, a non-programmer. Could you give
me hints to cope with this, please? Thank you very much for any replies!
Yours sincerely,
Chaofu Wu
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[gmx-users] How to restrain dihedral angles to reserve the tacticity?

2013-05-23 Thread Wu Chaofu
Dear gmxers,
I try to reserve the tacticity of polymer chains during the MD simulations.
By searching this mail-list, I find that to restrain dihedral angles
provides a way to realize it. However, what dihedral angles should I
restrain? For example, a polymer has a monomer with a chiral carbon C1 and
a non-chiral carbon C2 on the main chain, and two different side groups
(i.e. R1 and R2) are attached to C1. Could you give me some hints, please?
Thanks a lot for any reply to this letter.
Yours sincerely,
Chaofu Wu
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[gmx-users] position restrained energy minimization

2013-04-17 Thread Wu Chaofu
Dear gmxers,
As is well-known, molecular dynamics can be implemented with position
restrained in gromacs. Now I want to ensure whether energy minimization can
also be performed with position restrained. Thanks for any reply to this
letter.
Chaofu Wu
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[gmx-users] difference between the tabulated and Cut-off Electicstatics potentials

2012-10-06 Thread Wu Chaofu
Dear gmxers,
I am trying to perform two separate const-NPT MD simulations using
tablulated and Cut-off Electrostatics potentials. I find that for the
two cases the density of system is stablized at different values (1200
vs. 1400 g/cm3). Since the partial charges are all zeros in the top
files, I assume the two potentials generate same results. But why not
as expected? Could you please give me some hints?
Yours sincerely,
Chaofu Wu
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[gmx-users] Some tips for decreasing CPU time for mdrun -rerun

2012-09-20 Thread Wu Chaofu
Dear gmxers,
I have generated MD simulation trajectory using gmx, and now I want to
recalculate the energies and forces for the older trajectory by
excluding interactions between two defined groups. Therefore, the
older trajectory is used as one input option for mdrun through -rerun.
In my opinions, the newer run shoud much quicker than the older one
since only saved frames and less interactions are employed in this
calculation. However, I find that the speed is almost same. How to
decreasing CPU time for mdrun -rerun? I think I must have missed
something. Could you please give me some hints? Thank you a lot for
any reply.
Yours sincerely,
Chaofu Wu
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[gmx-users] Automatic calculations of forces in tabulated potentials?

2012-09-08 Thread Wu Chaofu
Dear gmxers,
Can the forces F(r) be calculated automatically from the potentials
E(r) so that they can be replaced initially by zeros in the tabulated
potentials? Thank you for any reply.
Yours sincerely,
Chaofu Wu
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[gmx-users] puzzling about ffnonbonded.itp

2012-09-03 Thread Wu Chaofu
Dear gmxers,
While I try to make one customed force field by studying some existing
force fields, I find that bond_type and at.num defining [atomtypes ]
in the ffnonbonded.itp are included in some force fields (i.e.
oplsaa), but not in other force fields (i.e gmx). I wonder how gmx
identifies the difference and choose the correct parameters from them.
Could you please expain this in details? Thank you very much for any
reply.
Yours sincerely,
Chaofu Wu
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[gmx-users] What is gbsa.itp in oplsaa of gmx4.5.5?

2012-09-02 Thread Wu Chaofu
Dear gmxers,
I am puzzling about the gbsa.itp file as listed below. What does each
item mean? Could you please explain it?
;atype  sar st pi gbr hct
opls_102 0.16 1 1.215 0.1625 0.79 ; N (RNH3+)

Yours sincerely,
Chaofu Wu
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[gmx-users] How to constrain some angles?

2012-07-24 Thread Wu Chaofu
Dear gmxers,
For some purpose, I want to constrain some angles. Note that it is
"some" but not "all", and "constrain" but not "restrain". How to do
with it? Thanks a lot for any reply.
Chaofu Wu
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[gmx-users] How to speed up equilibrating the density of bulk system?

2012-07-17 Thread Wu Chaofu
Dear gmxers,

I am trying to generate one polymer melt from one big enough box using
NPT MD in gmx. I find that the density of system varies very slow.
Could you please give me some hints about how to speed up this
process? Thanks a lot for any reply.

Yours sincerely,

Chaofu Wu.
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