[gmx-users] Using ATB to generate valid topologies

Wed Jul 13 17:02:32 CEST 2016

>> 
>> Just for the record ATB is a very good tool to build a start up topology. They also have a large set of topologies available on the site.
>> 
>> The charges are determined by QM and the user chooses the level of accuracy.
>> The bonded and LJ parameters are chosen based on the type of atom and it connectivity. Most atom types are already existing.
>> 
>> The sad part of ATB and other automated topology builders is that it is difficult to make a correct topology without putting the hands in.
>> 
>> Note that the CHARMM topology builder is even worst that ATB, but it gives you consistent topologies with existing ones.
>> 
> 
> Which CHARMM topology builder?  CGenFF or ParamChem?  I'd be curious to know the basis upon which this claim is made.  
My experience in building CHARMM topologies … building from existing topologies is rather coarse! 
> CHARMM and GROMOS follow very different parametrization protocols, so if a systematic analysis has been done, in the context of the relative accuracy of the parent force fields, I would really like to see the results.  I think that would be a very valuable effort.
Yes CGgenFF, it builds from building blocks and not clear to me how it adjusts the charges … but no QM!
> 
> Note that at least CGenFF gives penalty scores for all parameters that it provides the user, specifically telling which parameters will require additional work.
How does it determine them? 
No penalty does not guaranty good parameters but small expected deviation from existing topology … 
> 
>> In short: You need an experienced modeller to help you “validating” your topology.
>> 
> 
> Agreed 100%.  There is no black box method that is perfect or can be trusted implicitly.  Some are better than others, but force fields are as much an art as they are a science.  A perfect, hands-off method for parametrization of any molecule is, at present, untenable.
> 
> -Justin
> 
>> X-
>> 
>>> On 12 Jul 2016, at 14:40, David van der Spoel <spoel at xray.bmc.uu.se> wrote:
>>> 
>>> On 12/07/16 13:47, Justin Lemkul wrote:
>>>> 
>>>> 
>>>> On 7/11/16 9:52 AM, ALEXANDER DHALIWAL wrote:
>>>>> Dear GROMACS users,
>>>>> 
>>>>> I am pioneering the use of GROMACS in my lab to supplement some of our
>>>>> experimental research. I have generated some topologies from the
>>>>> Automated
>>>>> Topology Builder (ATB), but I am unsure whether or not to trust the files
>>>>> provided by this service. I am only an undergrad, so I would not feel
>>>>> comfortable asking my supervisor to invest thousands of dollars into a
>>>>> program such as Gaussian09 to validate these topologies. Does this
>>>> 
>>>> One would not use Gaussian to validate ATB topologies.  One would
>>>> generally *start* with a QM calculation to get charge distributions,
>>>> then validate against other data.  The problem with the GROMOS force
>>>> field is that there is little connection between QM calculations and the
>>>> final topologies.  I have posted at length on this topic just within the
>>>> last few days; please check the archive.
>>>> 
>>>>> community trust the outputs of ATB and, if not, could you provide me with
>>>>> suggestions as to how I may validate my topologies given my
>>>>> restraints? Any
>>>>> advice would be much appreciated.
>>>>> 
>>>> 
>>>> It depends on how complex the molecules are.  GROMOS parametrization is
>>>> empirical; existing building blocks are put together to yield a
>>>> molecule, and any unknown groups or strange linkages are explicitly
>>>> parametrized using model compounds.  I don't recall all the guts of what
>>>> ATB does (I haven't used the GROMOS force field in a long time) but I
>>>> believe it is doing this, coupled with a quick QM calculation for charge
>>>> refinement in the case that the constituent groups are not easily looked
>>>> up from an existing database).  In general, the topologies from ATB are
>>>> significantly better than from, e.g. PRODRG, but the skeptic/force field
>>>> purist in me never trusts a black box.  The problem, when it comes to
>>>> ligands/drugs is lack of target data.  For small molecules, there are
>>>> thermodynamic properties that one can look at.  For more complex things
>>>> like drugs, you might get lucky and have something like a logP tabulated
>>>> somewhere, but such data can often be difficult or impossible to obtain.
>>>> 
>>>> -Justin
>>>> 
>>> http://virtualchemistry.org provides validated topologies for about 150 compounds, that is force fields have been tested by running liquid simulations.
>>> 
>>> 
>>> --
>>> David van der Spoel, Ph.D., Professor of Biology
>>> Dept. of Cell & Molec. Biol., Uppsala University.
>>> Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205.
>>> spoel at xray.bmc.uu.se    http://folding.bmc.uu.se
>>> --
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>> 
> 
> -- 
> ==================================================
> 
> Justin A. Lemkul, Ph.D.
> Ruth L. Kirschstein NRSA Postdoctoral Fellow
> 
> Department of Pharmaceutical Sciences
> School of Pharmacy
> Health Sciences Facility II, Room 629
> University of Maryland, Baltimore
> 20 Penn St.
> Baltimore, MD 21201
> 
> jalemkul at outerbanks.umaryland.edu <mailto:jalemkul at outerbanks.umaryland.edu> | (410) 706-7441
> http://mackerell.umaryland.edu/~jalemkul <http://mackerell.umaryland.edu/~jalemkul>
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