[gmx-users] multiple time step

[chris.neale at utoronto.ca]

I recall seeing something online about how gromacs developers have  
decided to focus on increasing the overall speed and allowing  
generally large timesteps (via e.g. angle constraints) vs.  
implementing multiple timestepping (no mailing list ref. sorry). I  
agree that this is not a logically exclusive decision -- PME takes  
 >20% of the time so if they were doing it only 1/2 as often then  
there is the possibility of a real speedup. Nevertheless, it would  
need to be tested and perhaps the developers have indeed run these  
tests -- I've simply not seen the results. One would think, though,  
that PME could nearly always be done less often than, for example,  
bonded interactions.

I agree with Erik that the work would be large, but I disagree that  
the benefits would be small -- although I suspect that neither of us  
has any data to support such claims :).

Unfortunately, the bottom line is that this is free software and if  
you want it then you can code it. Or at the very least, you should  
benchmark the benefits on NAMD and then submit an "enhancement"  
bugzilla.

Chris.


-- original message --

The core developers have the answer for this one, but I can make an
educated guess:

Implementing it would mean a LOT of work and the rewards are small. The
latter because most particles will have rougly the same oscillation
period if one uses all-atom forcefields and turn on virtual sites and
constrains the bonds, hence the point of having multiple time steps is lost.

Vitaly Chaban skrev:
> Chris,
>
> An interesting question...
>
> BTW, is there any philosophy of gromacs developers to avoid this
> algorithm in the MD engine?
>
> Vitaly
>
>
>
>
>> multiple timesteps are not possible as far as gromacs 4.0.7. NAMD  
>> can do this.
>>
>>
>> -- original message --
>>
>> Is it possible to carry out  multiple time step  molecular
>> dynamics simulations
>> in Gromacs
>> 4.0. versions ? Could you
>> please give me some information about this issue ?
>>
>> Thank you very much for your attention.
>>