Re: Simulation in vaccum

From: Elijah Roberts (erobert3_at_scs.uiuc.edu)
Date: Sun Jan 08 2006 - 10:53:43 CST

Bo, this error message indicates that you are running the simulation
using constant pressure and looking at the config file you sent to the
list earlier, you are also using constant temp. Do you have a specific
reason for wanting to run in the NPT ensemble with a vacuum simulation?
I think that perhaps in a vacuum simulation you would be better off in
an NVE ensemble where you maintain a constant volume and energy. Do this
by setting the two values below:

langevin off
langevinPiston off

Keeping the volume constant should eliminate the error you were getting,
since the cell volume will no longer change.

Elijah

JC Gumbart wrote:
> Okay, then the error message must be non-specific (a minor inconsistency
> only). It actually is referring to how NAMD parallelizes the simulation
> space, so when it says "periodic cell", it must mean more generally "volume
> of simulated atoms". I think you are perfectly fine then in just setting
> "margin 1" at least for this portion of your simulation.
>
> If anyone knows definitively otherwise (I imagine only Jim would know at
> this point), please correct me.
>
>
> -----Original Message-----
> From: bo baker [mailto:bo.bybaker_at_gmail.com]
> Sent: Saturday, January 07, 2006 7:13 PM
> To: JC Gumbart
> Cc: namd-l_at_ks.uiuc.edu
> Subject: Re: namd-l: Simulation in vaccum
>
> I don't define any basis vectors in my conf file, and no line of PME.
> That is why I am very confused. May be the default setting in NAMD
> includes the cellBasis Vectors and PME. So I should add lines such as
> 'PME no' to avoid the periodic simulation? Or simply NAMD does not
> support vaccum simulation?
>
> Thanks for advices
>
> Bo
>
> On 1/6/06, JC Gumbart <gumbart_at_ks.uiuc.edu> wrote:
>
>> You may have defined basis vectors in your configuration file
>> (cellBasisVector1, etc). Try removing them as well as the cellOrigin and
>> wrapAll lines if you have them. These are the options that define a
>> periodic cell. You will also have to turn off PME since this only applies
>> to periodic simulation (remove all lines for PME or add "PME no").
>>
>> I think that will do the trick.
>>
>>
>> -----Original Message-----
>> From: owner-namd-l_at_ks.uiuc.edu [mailto:owner-namd-l_at_ks.uiuc.edu] On Behalf
>> Of bo baker
>> Sent: Friday, January 06, 2006 10:13 PM
>> To: Pedro Borkowski
>> Cc: namd-l_at_ks.uiuc.edu
>> Subject: Re: namd-l: Simulation in vaccum
>>
>> But I run the simulation in vacuum, no water added. Where the
>> 'Periodic cell' comes from? There is only protein there.
>>
>>
>>>> FATAL ERROR: Periodic cell has become too small for original patch
>>>>
> grid!
>
>>>> Possible solutions are to restart from a recent checkpoint,
>>>> increase margin, or disable useFlexibleCell for liquid simulation.
>>>>
>> I am very confused.
>>
>> Thanks for any advice.
>>
>> Bo
>>
>> On 1/6/06, Pedro Borkowski <pedro.borkowski_at_gmail.com> wrote:
>>
>>> hi,
>>>
>>> This was previously discussed
>>>
>>> http://www.ks.uiuc.edu/Research/namd/mailing_list/namd-l/2739.html
>>>
>>> hope this helps
>>>
>>> -Pedro
>>>
>>> On 1/6/06, bo baker <bo.bybaker_at_gmail.com> wrote:
>>>
>>>> Hello, NAMD:
>>>>
>>>> I built two models of a transmembrane protein based on two different
>>>> templates. I would like to do some initial structure refinments:
>>>> subject the two models to minimization and short simulation in vacuum.
>>>> This would allow me to compare the two models in energy level as well
>>>> as geometry level. After this, the model will be inserted into
>>>> membrane and water for
>>>> futher MD simulation.
>>>>
>>>> I am not sure if NAMD is good for this purpose, simulation protein
>>>> structure in vacuum. I couldn't find the tutorial or examples. I have
>>>> tried some steps, but the run was stopped prematured.
>>>>
>>>> Here is how I did:
>>>>
>>>> --- minimization for 2000 steps
>>>> --- equil at 310 K for 25000 steps
>>>>
>>>> Here are the error messages:
>>>> For model 1:
>>>>
>>>> WRITING COORDINATES TO DCD FILE AT STEP 24000
>>>> TIMING: 24100 CPU: 2850.66, 0.1199/step Wall: 3000.94,
>>>> 0.163925/step, 0.132051 hours remaining, 0 kB of memory in use.
>>>> ENERGY: 24100 543.6413 1486.1952 923.4096 =20
>>>> 80.5016 -2664.1032 -311.3172 0.0000 =20
>>>> 0.0000 1922.0600 1980.3873 315.5194 =20
>>>> 2010.7229 2002.7730 311.0336
>>>>
>>>> FATAL ERROR: Periodic cell has become too small for original patch
>>>>
> grid!
>
>>>> Possible solutions are to restart from a recent checkpoint,
>>>> increase margin, or disable useFlexibleCell for liquid simulation.
>>>>
>>>>
>>>> For model 2:
>>>>
>>>> TIMING: 3200 CPU: 533.74, 0.1147/step Wall: 571.251, 0.121714/step,
>>>> 0.804667 hours remaining, 0 kB of memory in use.
>>>> ENERGY: 3200 566.7572 1603.5447 1048.2289 =20
>>>> 107.6930 -2211.1402 -255.1635 0.0000 =20
>>>> 0.0000 2051.3032 2911.2233 312.3809 =20
>>>> 2941.2697 2943.5047 311.9550
>>>>
>>>> FATAL ERROR: Periodic cell has become too small for original patch
>>>>
> grid!
>
>>>> Possible solutions are to restart from a recent checkpoint,
>>>> increase margin, or disable useFlexibleCell for liquid simulation.
>>>>
>>>> I compare the TOTAL and rmsd of the two run. TOTAL are arond 1980
>>>> (model 1) and 2840 (model 2), rmsd are around 2.31 (model 1) and
>>>> 2.341 (model 2). When I exam the trajectories, both structures move
>>>> around entirely but no big change in conformation.
>>>>
>>>> Thank you for advice!
>>>>
>>>> Regards
>>>>
>>>> Bo
>>>>
>>>>
>>>>
>>> --
>>> -Pedro Borkowski
>>>
>>>
>>
>>
>
>
>

This archive was generated by hypermail 2.1.6 : Wed Feb 29 2012 - 15:41:30 CST