[gmx-users] NPT equilibration in KALP15-DPPC

[Justin Lemkul]

On 8/27/12 2:30 AM, Shima Arasteh wrote:
>
>
>   Hi,
>
> After the NPT mdrun, I visulized the npt.gro.
> I need to know if this npt.gro is the final result of equilibration?

 From mdrun -h:

"The structure file (-c) contains the coordinates and velocities of the last step."

> I see 2,3 water molecules between the lipid chains. Should I remove them? Can I remove them? Or it's not the step that I can make such a decision?
>

You can remove them.  Update the topology and the number of atoms at the top of 
the .gro file, then re-equilibrate.

-Justin

> Thanks in advance.
>
> Sincerely,
> Shima
>
>
> ----- Original Message -----
> From: Justin Lemkul <jalemkul at vt.edu>
> To: Shima Arasteh <shima_arasteh2001 at yahoo.com>; Discussion list for GROMACS users <gmx-users at gromacs.org>
> Cc:
> Sent: Sunday, August 26, 2012 5:29 PM
> Subject: Re: [gmx-users] NPT equilibration in KALP15-DPPC
>
>
>
> On 8/26/12 8:54 AM, Shima Arasteh wrote:
>>
>>
>> Hi,
>>
>> For NPT equilibration of KALP15 in DPPC following the Justin's tutorial, when
>> I run the grompp command, I get 4 notes. Is it necessary to pay attention to
>> the notes ? Are they notable?
>>
>
> Notes are generally notable, yes ;)  Never ignore anything grompp tells you,
> that's my rule of thumb.  Some messages are less critical than others.  The ones
> shown here are quite important.
>
> These warnings cannot possibly be produced by the .mdp file in the tutorial, and
> they suggest that you are not doing NPT under any sort of stable conditions.
> You're using plain cutoffs, no constraints, and attempting to produce NVE, which
> will surely fail.
>
> -Justin
>
>>
>> NOTE 1 [file npt.mdp]: You are using a cut-off for VdW interactions with NVE,
>> for good energy conservation use vdwtype = Shift (possibly with DispCorr)
>>
>>
>> NOTE 2 [file npt.mdp]: You are using a cut-off for electrostatics with NVE,
>> for good energy conservation use coulombtype = PME-Switch or
>> Reaction-Field-zero
>>
>> Generated 837 of the 2346 non-bonded parameter combinations Excluding 3
>> bonded neighbours molecule type 'Protein' Excluding 3 bonded neighbours
>> molecule type 'DPPC' Excluding 2 bonded neighbours molecule type 'SOL'
>> Excluding 1 bonded neighbours molecule type 'CL'
>>
>> NOTE 3 [file topol.top, line 929]: The bond in molecule-type Protein between
>> atoms 4 N and 5 H has an estimated oscillational period of 1.0e-02 ps, which
>> is less than 10 times the time step of 1.0e-03 ps. Maybe you forgot to change
>> the constraints mdp option.
>>
>> Number of degrees of freedom in T-Coupling group rest is 33897.00
>>
>> NOTE 4 [file npt.mdp]: You are using a plain Coulomb cut-off, which might
>> produce artifacts. You might want to consider using PME electrostatics.
>>
>>
>> Reading Coordinates, Velocities and Box size from old trajectory Will read
>> whole trajectory Last frame         -1 time  100.000 Using frame at t = 100
>> ps Starting time for run is 0 ps Largest charge group radii for Van der
>> Waals: 0.239, 0.234 nm Largest charge group radii for Coulomb:       0.239,
>> 0.234 nm This run will generate roughly 1 Mb of data
>>
>> There were 4 notes
>>
>> Thanks for your suggestions in advance.
>>
>> Sincerely, Shima
>>
>

-- 
========================================

Justin A. Lemkul, Ph.D.
Research Scientist
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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