A few things that may hopefully address your problems:
1.) Magnesium parameters are generally considered to be highly application
dependent. I don't think anyone in the AMBER community has advocated a
single "best" set yet. You probably want to carefully search the
literature and run some basic tests before settling on a model. It
probably won't be one that is released with AMBER (i.e. is already in a
parm or frcmod file).
2.) In my opinion, and others here might agree, 5000 steps of minimization
is rather extraneous and probably more likely to cause new problems than
resolve old ones. 1000 TOTAL is probably a more useful value.
3.) I'm not sure what you were meaning to do with your heating. As is, you
are specifying 0 initial temperature (tempi) so that all velocities are
zero (probably not good). The reference temperature (temp0) will probably
be ignored since you specified NVE dynamics (ntt=1), but I don't know for
sure.
There are many many heating procedures that you could use, but I don't know
enough to recommend you a specific. For small molecules I've had
reasonable success with just starting at the desired temperature, but I
think that may fail for larger systems, especially if the initial
coordinates are from a low temperature crystal structure.
Regards,
Brian
On Tue, Dec 13, 2011 at 9:23 AM, Xiaozhou Li <xli12.qub.ac.uk> wrote:
> Dear AMBER users,
>
> I'm now working on a MD simulation to an enzyme which has peculiar
> ligands. Followed the official tutorial which dealing with non-standard
> residue (link: http://ambermd.org/tutorials/advanced/tutorial1_adv/) I
> created a new residue "ATP" which contains an ATP as well as a magnesium
> ion (nominated as "MG" and it does not exist in the library).
>
> The template of the new residue was first generated by Gaussian 09 (by
> single point charge calculation), then use "antechamber" in AMBER to shift
> it into ".mol2" format, which contains atom charges and connection
> information, etc. A ".frcmod" file was created simultaneously, said that
> the MASS and NONBON parameters of MG should be revised. MASS was pretty
> easy to obtain, NONBON was directly use those original information in AMBER
> lib.
>
> In "tleap", the residue I manually created was imported directly by the
> command "loadmol2". The final model for simulation was then successfully
> generated. The minimization step was OK, using 5000 step of SD method as
> well as 5000 step of CONJ method without restriction to the protein. Issue
> occurred when it came to the starting point of heating step:
>
> (the last lines in the output file)
> vlimit exceeded for step 3; vmax = 21.5763
> vlimit exceeded for step 4; vmax = 115.6802
> vlimit exceeded for step 5; vmax = 221.8382
> vlimit exceeded for step 6; vmax = 74.7778
> vlimit exceeded for step 7; vmax = 42.8791
>
> Here are the ".frcmod" file and my MD input condition:
>
>
>
> (.frcmod file)
>
> ------------------------------------------------
> remark goes here
> MASS
> MG 24.305
>
> BOND
>
> ANGLE
>
> DIHE
>
> IMPROPER
> c3-ca-na-cc 1.1 180.0 2.0 Using default
> value
> h5-na-cc-nd 1.1 180.0 2.0 Using default
> value
> ca-ca-ca-nd 1.1 180.0 2.0 Using default
> value
> ca-nb-ca-nh 1.1 180.0 2.0 Using default
> value
> ca-hn-nh-hn 1.1 180.0 2.0 Using default
> value
> h5-nb-ca-nb 1.1 180.0 2.0 Using default
> value
> ca-na-ca-nb 1.1 180.0 2.0 Using default
> value
>
> NONBON
> MG 0.7926 0.8947 ATTN, need revision
> ------------------------------------------------
> (MD input file)
> ------------------------------------------------
> Heating
> &cntrl
> imin=0,irest=0,ntx=1,ntb=1,
> cut=10.0,ntr=1,restraint_wt=0.5,restraintmask=':1-395',
> ntc=2,ntf=2,
> tempi=0.0,temp0=300.0,
> ntt=1,nstlim=50000,dt=0.001,ntpr=100,ntwx=100,ntwr=200
>
> I'm pretty appreciated if anyone could help me to get through that issue.
>
> P.S. In my previous work, I utilized the normal template which exist in
> the AMBER lib (name: MG2) for the magnesium ion. The template of ATP did
> not contain the magnesium ion. The ".frcmod" file corresponding to ATP was
> just as the one I provided above, but without information on MG. Everything
> went fine from minimization to heating, equilibration and MD simulation
> with NPT ensemble. Hopefully what I mention here make sense.
>
> Many thanks,
> Xiaozhou
> _______________________________________________
> AMBER mailing list
> AMBER.ambermd.org
> http://lists.ambermd.org/mailman/listinfo/amber
>
--
================================ Current Address =======================
Brian Radak : BioMaPS
Institute for Quantitative Biology
PhD candidate - York Research Group : Rutgers, The State
University of New Jersey
University of Minnesota - Twin Cities : Center for Integrative
Proteomics Room 308
Graduate Program in Chemical Physics : 174 Frelinghuysen Road,
Department of Chemistry : Piscataway, NJ
08854-8066
radak004.umn.edu :
radakb.biomaps.rutgers.edu
====================================================================
Sorry for the multiple e-mail addresses, just use the institute appropriate
address.
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Received on Tue Dec 13 2011 - 07:30:03 PST
